Introduction to Java ( Basics of Java Programming)
0 likes104 views
Introduction to Java Programming Basics of Java Programming
![25
Arvind
Bhave
FIRST JAVA PROGRAM
/*
This is a simple Java program.
Call this file "Example.java".
*/
class Example {
// Your program begins with a call to main().
public static void main(String args[]) {
System.out.println("This is a simple Java program.");
}
}](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-25-320.jpg)
![29
Arvind
Bhave
IF STATEMENT
. Here are a few Operator
< Less than
> Greater than
== Equal to
Notice that the test for equality is the double equal sign.
a program that illustrates the if statement:
/* Demonstrate the if Call this file "IfSample.java". */
class IfSample {
public static void main(String args[]) {
int x, y;
x = 10; y = 20;
if(x < y) System.out.println("x is less than y");
x = x * 2;
if(x == y) System.out.println("x now equal to y");
x = x * 2;
if(x > y) System.out.println("x now greater than y");
// this won't display anything
if(x == y) System.out.println("you won't see this");
}
}](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-29-320.jpg)
![32
Arvind
Bhave
THE FOR LOOP
Here is a short program that illustrates the for loop:
/*Demonstrate the for loop. Call this file "ForTest.java". */
class ForTest {
public static void main(String args[]) {
int x;
for(x = 0; x<5; x = x+1)
System.out.println("This is x: " + x);
}
}
This program generates the following output:
This is x: 0
This is x: 1
This is x: 2
This is x: 3
This is x: 4](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-32-320.jpg)
![35
Arvind
Bhave
USING BLOCKS OF CODE
Let’s look at another example. The following program uses a block of code as the
target of a for loop.
/* Demonstrate a block of code. Call this file "BlockTest.java“ */
class BlockTest {
public static void main(String args[]) {
int x, y;
y = 20;
// the target of this loop is a block
for(x = 0; x<10; x++) {
System.out.println("This is x: " + x);
System.out.println("This is y: " + y);
y = y - 2;
}
}
}](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-35-320.jpg)
![40
Arvind
Bhave
DATA TYPES
Long
The range of a long is quite large. This makes it useful when big, whole numbers are
needed. For example, here is a program that computes the number of miles that light will
travel in a specified number of days.
// Compute distance light travels using long variables.
class Light {
public static void main(String args[]) {
int lightspeed;
long days;
long seconds;
long distance;
// approximate speed of light in miles per second
lightspeed = 186000;
days = 1000; // specify number of days here
seconds = days * 24 * 60 * 60; // convert to seconds
distance = lightspeed * seconds; // compute distance
System.out.print("In " + days);
System.out.print(" days light will travel about ");
System.out.println(distance + " miles.");
}
}
This program generates the following output:
In 1000 days light will travel about 16070400000000 miles.](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-40-320.jpg)
![43
Arvind
Bhave
DATA TYPES
Here is a short program that uses double variables
to compute the area of a circle:
// Compute the area of a circle.
class Area {
public static void main(String args[]) {
double pi, r, a;
r = 10.8; // radius of circle
pi = 3.1416; // pi, approximately
a = pi * r * r; // compute area
System.out.println("Area of circle is " + a);
}
}](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-43-320.jpg)
![45
Arvind
Bhave
DATA TYPES
// Demonstrate char data type.
class CharDemo {
public static void main(String args[]) {
char ch1, ch2;
ch1 = 88; // code for X
ch2 = 'Y';
System.out.print("ch1 and ch2: ");
System.out.println(ch1 + " " + ch2);
ch1 = 'X';
System.out.println("ch1 contains " + ch1);
ch1++; // increment ch1
System.out.println("ch1 is now " + ch1);
}
}](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-45-320.jpg)
![47
Arvind
Bhave
DATA TYPES
// Demonstrate boolean values.
class BoolTest {
public static void main(String args[]) {
boolean b;
b = false;
System.out.println("b is " + b);
b = true;
System.out.println("b is " + b);
// a boolean value can control the if statement
if(b) System.out.println("This is executed.");
b = false;
if(b) System.out.println("This is not executed.");
// outcome of a relational operator is a boolean value
System.out.println("10 > 9 is " + (10 > 9));
}
}
The output generated by this program is shown here:
b is false
b is true
This is executed.
10 > 9 is true](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-47-320.jpg)
![48
Arvind
Bhave
VARIABLES
The variable is the basic unit of storage
A variable is defined by the combination of an
identifier, a type, and an optional initializer.
All variables have a scope, which defines their
visibility, and a lifetime.
Declaring a Variable
In Java, all variables must be declared before they can
be used.
The basic form of a variable declaration
type identifier [ = value][, identifier [= value] ...] ;
The type is one of Java’s atomic types, or the name of a
class or interface
The identifier is the name of the variable](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-48-320.jpg)
![50
Arvind
Bhave
DYNAMIC INITIALIZATION
Java allows variables to be initialized dynamically, using any
expression valid at the time the variable is declared.
For example, here is a short program that computes the length of
the hypotenuse of a right triangle given the lengths of its two
opposing sides:
// Demonstrate dynamic initialization.
class DynInit {
public static void main(String args[]) {
double a = 3.0, b = 4.0;
// c is dynamically initialized
double c = Math.sqrt(a * a + b * b);
System.out.println("Hypotenuse is " + c);
}
}
Here, three local variables—a, b,and c—are declared. The first
two, a and b, are initialized by constants. However, c is
initialized dynamically to the length of the hypotenuse
(using the Pythagorean theorem).](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-50-320.jpg)
![51
Arvind
Bhave
THE SCOPE AND LIFETIME OF
VARIABLES
Java allows variables to be declared within any block
A block is begun with an opening curly brace and ended by a closing curly brace.
A block defines a scope. Thus, each time you start a new block, you are creating a
new scope.
// Demonstrate block scope.
class Scope {
public static void main(String args[]) {
int x; // known to all code within main
x = 10;
if(x == 10) { // start new scope
int y = 20; // known only to this block
// x and y both known here.
System.out.println("x and y: " + x + " " + y);
x = y * 2;
}
// y = 100; // Error! y not known here
// x is still known here.
System.out.println("x is " + x);
}
}](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-51-320.jpg)
![52
Arvind
Bhave
LIFETIME OF A VARIABLE.
// Demonstrate lifetime of a variable.
class LifeTime {
public static void main(String args[]) {
int x;
for(x = 0; x < 3; x++) {
int y = -1; // y is initialized each time block is entered
System.out.println("y is: " + y); // this always prints -1
y = 100;
System.out.println("y is now: " + y);
}
}
}
The output generated by this program is shown here:
y is: -1
y is now: 100
y is: -1
y is now: 100
y is: -1
y is now: 100](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-52-320.jpg)
![58
Arvind
Bhave
CASTING INCOMPATIBLE TYPES
The following program demonstrates some type conversions that require casts:
// Demonstrate casts.
class Conversion {
public static void main(String args[]) {
byte b;
int i = 257;
double d = 323.142;
System.out.println("nConversion of int to byte.");
b = (byte) i;
System.out.println("i and b " + i + " " + b);
System.out.println("nConversion of double to int.");
i = (int) d;
System.out.println("d and i " + d + " " + i);
System.out.println("nConversion of double to byte.");
b = (byte) d;
System.out.println("d and b " + d + " " + b);
}
}](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-58-320.jpg)
![64
Arvind
Bhave
THE TYPE PROMOTION RULES
The following program demonstrates how each value in the expression
gets promoted to match the second argument to each binary operator:
class Promote {
public static void main(String args[]) {
byte b = 42;
char c = 'a';
short s = 1024;
int i = 50000;
float f = 5.67f;
double d = .1234;
double result = (f * b) + (i / c) - (d * s);
System.out.println((f * b) + " + " + (i / c) + " - " + (d * s));
System.out.println("result = " + result);
}
}](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-64-320.jpg)
![67
Arvind
Bhave
ONE-DIMENSIONAL ARRAYS
A one-dimensional array is, essentially, a list of like-typed
variables.. The general form of a one dimensional array
declaration is
type var-name[ ];
Here, type declares the base type of the array. The base
type determines the data type of each element that
comprises the array.
For example, the following declares an array
named month_days with the type “array of int”:
int month_days[];
Although this declaration establishes the fact that
month_days is an array variable, no array actually
exists. In fact, the value of month_days is set to null,
which represents an array with no value.](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-67-320.jpg)
![68
Arvind
Bhave
ONE-DIMENSIONAL ARRAYS
To link month_days with an actual, physical
array of integers, you must allocate one using
new and assign it to month_days. new is a
special operator that allocates memory.
The general form of new as it applies to one-
dimensional arrays appears as follows:
array-var = new type[size];
Here, type specifies the type of data being
allocated, size specifies the number of elements in
the array, and array-var is the array variable
that is linked to the array.](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-68-320.jpg)
![69
Arvind
Bhave
ONE-DIMENSIONAL ARRAYS
This example allocates a 12-element array of
integers and links them to month_days.
month_days = new int[12];
After this statement executes, month_days will
refer to an array of 12 integers. Further, all
elements in the array will be initialized to zero.](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-69-320.jpg)
![70
Arvind
Bhave
ONE-DIMENSIONAL ARRAYS
Here is one more example that uses a one-dimensional
array. It finds the average of a set of numbers.
// Average an array of values.
class Average {
public static void main(String args[]) {
double nums[] = {10.1, 11.2, 12.3, 13.4, 14.5};
double result = 0;
int i;
for(i=0; i<5; i++)
result = result + nums[i];
System.out.println("Average is " + result / 5);
}
}](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-70-320.jpg)
![71
Arvind
Bhave
MULTIDIMENSIONAL ARRAYS
In Java, multidimensional arrays are actually
arrays of arrays. These, as you might expect, look
and act like regular multidimensional arrays.
For example, the following declares a two-
dimensional array variable called twoD.
int twoD[][] = new int[4][5];
This allocates a 4 by 5 array and assigns it to
twoD. Internally this matrix is implemented
as an array of arrays of int.](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-71-320.jpg)
![72
Arvind
Bhave
// Demonstrate a two-dimensional array.
class TwoDArray {
public static void main(String args[]) {
int twoD[][]= new int[4][5];
int i, j, k = 0;
for(i=0; i<4; i++)
for(j=0; j<5; j++) {
twoD[i][j] = k;
k++;
}
for(i=0; i<4; i++) {
for(j=0; j<5; j++)
System.out.print(twoD[i][j] + " ");
System.out.println();
}
}
}](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-72-320.jpg)
![74
Arvind
Bhave
2 D ARRAY
It is possible to initialize multidimensional arrays.
Enclose each dimension’s initializer within its own
set of curly braces.
Initialization of 2 D Array
double m[][] = {
{ 0*0, 1*0, 2*0, 3*0 },
{ 0*1, 1*1, 2*1, 3*1 },
{ 0*2, 1*2, 2*2, 3*2 },
{ 0*3, 1*3, 2*3, 3*3 }
};
0*0=column*row](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-74-320.jpg)
![75
Arvind
Bhave
ALTERNATIVE ARRAY
DECLARATION SYNTAX
There is a second form that may be used to declare
an array:
type[ ] var-name;
Here, the square brackets follow the type specifier,
and not the name of the array variable. For ex, the
following two declarations are equivalent:
int al[] = new int[3];
int[] a2 = new int[3];
The following declarations are also equivalent:
char ch1[][] = new char[3][4];
char[][] ch2 = new char[3][4];](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-75-320.jpg)
![85
Arvind
Bhave
// Demonstrate if-else-if statements.
class IfElse {
public static void main(String args[]) {
int month = 4; // April
String season;
if(month == 12 || month == 1 || month == 2)
season = "Winter";
else if(month == 3 || month == 4 || month == 5)
season = "Spring";
else if(month == 6 || month == 7 || month == 8)
season = "Summer";
else if(month == 9 || month == 10 || month == 11)
season = "Autumn";
else
season = "Bogus Month";
System.out.println("April is in the " + season + ".");
}
}](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-85-320.jpg)
![87
Arvind
Bhave
A simple example of the switch.
class SampleSwitch {
public static void main(String args[]) {
for(int i=0; i<6; i++)
switch(i) {
case 0:
System.out.println("i is zero.");
break;
case 1:
System.out.println("i is one.");
break;
case 2:
System.out.println("i is two.");
break;
case 3:
System.out.println("i is three.");
break;
default:
System.out.println("i is greater than 3.");
}
}
}](https://image.slidesharecdn.com/javaslidesu-1-250624065305-08c98588/85/Introduction-to-Java-Basics-of-Java-Programming-87-320.jpg)
Introduction to Java ( Basics of Java Programming)
- 1. Arvind Bhave 1 INTRODUCTION TO JAVA Arvind M Bhave RTMNU
- 2. 2 Arvind Bhave JAVA-INTRODUCTION History Primary aim to develop small comp. language for consumer devices like Microwave Ovens, remote control, cable TV switch Boxes etc. Object-Oriented language developed by Sun Microsystem (USA) in 1991. Originally called “Oak” by James Gosling. Renamed to “Java” in 1995.
- 3. 3 Arvind Bhave JAVA PROGRAM- TYPES Application Applet Servlet
- 4. 4 Arvind Bhave JAVA PROGRAM- APPLICATION Application Program that runs on your computer under the operating system of that computer . Application programs are mostly in the form of character user interface (like C or C++). Also in the form of GUI for Windows Environment.
- 5. 5 Arvind Bhave JAVA PROGRAM- APPLET Tiny Java program Mainly used for Internet applications. Run on a web page. Applets programs are used to make animations, display images and run the sound also. React the user input and dynamically changed.
- 6. 6 Arvind Bhave JAVA PROGRAM- SERVLETS A mini server side program Similar to applets It is defined in the Java servlet API Particularly used for producing dynamic web contents.
- 7. 7 Arvind Bhave JAVA FEATURES 1. Simple 2. Secure 3. Portable 4. Object-oriented 5. Robust 6. Multithreaded 7. Architecture-Neutral 8. Compiled & Interpreted 9. High Performance 10. Distributed 11. Dynamic
- 8. 8 Arvind Bhave JAVA FEATURES Simple :- If you know C++, then moving to Java is easy Java inherits the C/C++ syntax. Need to learn OOP concept. Need to have some programming experience Designed for professional programmer.
- 9. 9 Arvind Bhave JAVA FEATURES Secure:- Risk of viral infection while downloading Some malicious program also exists. These programs gather private information like credit card no., passwords For these, Java provides a “firewall” between networked application and your computer Can safely download Java Applet. No use of pointers.
- 10. 10 Arvind Bhave JAVA FEATURES Portable :- Ensures portability in two ways First- Java compiler generates Byte code that can be implemented on any machine. Second- Size of primitive data types are machine independent.
- 11. 11 Arvind Bhave JAVA FEATURES Object Oriented:- All program code & data resides within objects and classes. Java contains set of classes arranged in packages, that can be use in program by inheritance. Truly object oriented.
- 12. 12 Arvind Bhave JAVA FEATURES Robust:- Java is strictly typed language It checks code compile time & run time (checking for data types) Consider two main reasons for program failure Memory management and mishandled exceptional conditions (i.e. run time errors) Java virtually eliminates memory management by managing allocations & de allocations of memory. Java provides Object oriented exceptional handling. Therefore Java is Robust.
- 13. 13 Arvind Bhave JAVA FEATURES MultiThreaded :- Handling multiple tasks simultaneously. You can write programs that do many things simultaneously Java supports multithreaded programming.
- 14. 14 Arvind Bhave JAVA FEATURES Architectural Neutral:- Changes and up gradation in O.S., processors & system resources will not force any changes in java programs. It is “write once; run anywhere, anytime, forever “. (this is goal) Means platform Independent.
- 15. 15 Arvind Bhave JAVA FEATURES Compiled & interpreted :- Java compiler translates source code into bytecode instructions. Bytecodes are not machine instructions. This bytecode is interpreted on any system having JVM.
- 16. 16 Arvind Bhave JAVA FEATURES High performance :- Java designed to perform well on a very low power CPUs. Java’s bytecode was carefully designed so that it would be easy to translate directly into native machine code.
- 17. 17 Arvind Bhave JAVA FEATURES Distributed:- Designed for distributed environment of the internet because it handles TCP/IP protocols. Java application can open & access remote objects on internet (like local system).
- 18. 18 Arvind Bhave JAVA FEATURES Dynamic:- Java program carry with them run-time type information. Due to this, it is possible to link the code dynamically in a safe manner.
- 19. 19 Arvind Bhave SOME OOP CONCEPT Data Abstraction:- Procedure of representing essential things without including details. Example 1- a computer is made of several part like CPU, keyboard, mouse etc. but we can think it as a single unit. Example 2- a car is a single object but it has several parts. Classes use theory of abstraction.
- 20. 20 Arvind Bhave SOME OOP CONCEPT Encapsulation:- The packing of data & functions into a single unit or component. class is an example of encapsulation. A class contains data & member functions (methods) common to all objects. Each member is private or public. Any non member function can not access the data of the class.
- 21. 21 Arvind Bhave SOME OOP CONCEPT Inheritance:- Is the method by which object of one class get the properties of another class. Provides the thought of reusability. We can add the new properties to the existing class without changing it. This can be achieved by deriving new class form existing one.
- 22. 22 Arvind Bhave SOME OOP CONCEPT Inheritance example:- RED YELLOW BLUE ORANGE GREEN VIOLET YELLOW ISH BROWN REDDIS H BROWN BLUISH BROWN
- 23. 23 Arvind Bhave SOME OOP CONCEPT Polymorphism :- (many forms) Allows the same function to act differently in different classes. Ability to take more than one form. Ability of giving same name to methods in different subclasses.
- 24. 24 Arvind Bhave SOME OOP CONCEPT Polymorphism example – Line Display() Dotted object Display(dotted) Single object Display(Single) Dash object Display(dash)
- 25. 25 Arvind Bhave FIRST JAVA PROGRAM /* This is a simple Java program. Call this file "Example.java". */ class Example { // Your program begins with a call to main(). public static void main(String args[]) { System.out.println("This is a simple Java program."); } }
- 26. 26 Arvind Bhave COMPILING THE PROGRAM execute the compiler, javac, specifying the name of the source file on the command line, as shown here: C:>javac Example.java The javac compiler creates a file called Example.class that contains the bytecode version of the program. The Java bytecode contains instructions the Java interpreter will execute. To actually run the program, you must use the Java interpreter, called java. C:>java Example When the program is run, the following output is displayed: This is a simple Java program
- 27. 27 Arvind Bhave COMPILING THE PROGRAM When Java source code is compiled, each individual class is put into its own output file named after the class and using the .class extension. This is why it is a good idea to give your Java source files the same name as the class they contain— the name of the source file will match the name of the .class file. When you execute the Java interpreter as just shown, you are actually specifying the name of the class that you want the interpreter to execute. It will automatically search for a file by that name that has the .class extension. If it finds the file, it will execute the code contained in the specified class.
- 28. 28 Arvind Bhave IF STATEMENT if statement works much like the IF statement in any other language. simplest form is if(condition) statement; Here, condition is a Boolean expression. If condition is true, then the statement is executed. If condition is false, then the statement is bypassed. Here is an example: if(num < 100) println("num is less than 100"); In this case, if num contains a value that is less than 100, the conditional expression is true, and println( ) will execute. If num contains a value greater than or equal to 100, then the println( ) method is bypassed.
- 29. 29 Arvind Bhave IF STATEMENT . Here are a few Operator < Less than > Greater than == Equal to Notice that the test for equality is the double equal sign. a program that illustrates the if statement: /* Demonstrate the if Call this file "IfSample.java". */ class IfSample { public static void main(String args[]) { int x, y; x = 10; y = 20; if(x < y) System.out.println("x is less than y"); x = x * 2; if(x == y) System.out.println("x now equal to y"); x = x * 2; if(x > y) System.out.println("x now greater than y"); // this won't display anything if(x == y) System.out.println("you won't see this"); } }
- 30. 30 Arvind Bhave IF STATEMENT The output generated by this program is shown x is less than y x now equal to y x now greater than y Notice one other thing in this program. The line int x, y; declares two variables, x and y, by use of a comma- separated list.
- 31. 31 Arvind Bhave THE FOR LOOP The simplest form of the for loop is shown here: for(initialization; condition; iteration) statement; In common form, the initialization portion of the loop sets a loop control variable to an initial value. The condition is a Boolean expression that tests the loop control variable. If the outcome of that test is true, the for loop continues to iterate. If it is false, the loop terminates. The iteration expression determines how the loop control variable is changed each time the loop iterates.
- 32. 32 Arvind Bhave THE FOR LOOP Here is a short program that illustrates the for loop: /*Demonstrate the for loop. Call this file "ForTest.java". */ class ForTest { public static void main(String args[]) { int x; for(x = 0; x<5; x = x+1) System.out.println("This is x: " + x); } } This program generates the following output: This is x: 0 This is x: 1 This is x: 2 This is x: 3 This is x: 4
- 33. 33 Arvind Bhave THE FOR LOOP In this example, x is the loop control variable. It is initialized to zero in the initialization portion of the for. At the start of each iteration (including the first one), the conditional test x < 10 is performed. If the outcome of this test is true, the println( ) statement is executed, and then the iteration portion of the loop is executed. This process continues until the conditional test is false. The increment operator increases its operand by one.
- 34. 34 Arvind Bhave USING BLOCKS OF CODE Java allows two or more statements to be grouped into blocks of code, also called code blocks. This is done by enclosing the statements between opening and closing curly braces. Once a block of code has been created, it becomes a logical unit that can be used any place that a single statement can. For example, a block can be a target for Java’s if and for statements. Consider this if statement: if(x < y) { // begin a block x = y; y = 0; } // end of block Here, if x is less than y, then both statements inside the block will be executed. Thus, the two statements inside the block form a logical unit, and one statement cannot execute without the other also executing. The key point here is that whenever you need to logically link two or more statements, you do so by creating a block.
- 35. 35 Arvind Bhave USING BLOCKS OF CODE Let’s look at another example. The following program uses a block of code as the target of a for loop. /* Demonstrate a block of code. Call this file "BlockTest.java“ */ class BlockTest { public static void main(String args[]) { int x, y; y = 20; // the target of this loop is a block for(x = 0; x<10; x++) { System.out.println("This is x: " + x); System.out.println("This is y: " + y); y = y - 2; } } }
- 36. 36 Arvind Bhave USING BLOCKS OF CODE The output generated by this program is shown here: This is x: 0 This is y: 20 This is x: 1 This is y: 18 This is x: 2 This is y: 16 This is x: 3 This is y: 14 This is x: 4 This is y: 12 This is x: 5 This is y: 10 This is x: 6 This is y: 8 This is x: 7 This is y: 6 This is x: 8 This is y: 4 This is x: 9 This is y: 2 In this case, the target of the for loop is a block of code and not just a single statement. Thus, each time the loop iterates, the three statements inside the block will be executed.
- 37. 37 Arvind Bhave DATA TYPES Java is strongly Typed Language First, every variable has a type, every expression has a type, and every type is strictly defined. Second, all assignments, whether explicit or via parameter passing in method calls, are checked for type compatibility. The Java compiler checks all expressions and parameters to ensure that the types are compatible. Any type mismatches are errors that must be corrected before the compiler will finish compiling the class. For example, in C/C++ you can assign a floating- point value to an integer. In Java, you cannot.
- 38. 38 Arvind Bhave DATA TYPES Data types can be put into 4 groups. Integers : This group includes byte, short, int, and long, which are for wholevalued signed numbers. Floating point : includes float and double, which represent numbers with fractional precision. Characters : includes char, represents symbols in a character set, like letters and numbers. Boolean : includes boolean, which is a special type for representing true/false values.
- 39. 39 Arvind Bhave DATA TYPES (INTEGERS) byte, short, int, and long All of these are signed, positive and negative values. Java does not support unsigned, positive-only integers. Name Width Range byte 8 –128 to 127 short 16 –32,768 to 32,767 int 32 –2,147,483,648 to 2,147,483,647 long 64 –9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
- 40. 40 Arvind Bhave DATA TYPES Long The range of a long is quite large. This makes it useful when big, whole numbers are needed. For example, here is a program that computes the number of miles that light will travel in a specified number of days. // Compute distance light travels using long variables. class Light { public static void main(String args[]) { int lightspeed; long days; long seconds; long distance; // approximate speed of light in miles per second lightspeed = 186000; days = 1000; // specify number of days here seconds = days * 24 * 60 * 60; // convert to seconds distance = lightspeed * seconds; // compute distance System.out.print("In " + days); System.out.print(" days light will travel about "); System.out.println(distance + " miles."); } } This program generates the following output: In 1000 days light will travel about 16070400000000 miles.
- 41. 41 Arvind Bhave DATA TYPES Floating-Point Types For example, calculations such as square root, or transcendentals such as sine and cosine, result in a value whose precision requires a floating-point type. Name Width in Bits Approximate Range double 64 4.9e–324 to 1.8e+308 float 32 1.4e−045 to 3.4e+038
- 42. 42 Arvind Bhave DATA TYPES float The type float specifies a single-precision value that uses 32 bits of storage Double uses 64 bits to store a value. Double precision is actually faster than single precision. All transcendental math functions, such as sin( ), cos( ), and sqrt( ), return double values. When you need to maintain accuracy over many iterative calculations, or are manipulating large-valued numbers, double is the best choice
- 43. 43 Arvind Bhave DATA TYPES Here is a short program that uses double variables to compute the area of a circle: // Compute the area of a circle. class Area { public static void main(String args[]) { double pi, r, a; r = 10.8; // radius of circle pi = 3.1416; // pi, approximately a = pi * r * r; // compute area System.out.println("Area of circle is " + a); } }
- 44. 44 Arvind Bhave DATA TYPES Char Java uses Unicode to represent characters. Unicode defines a fully international character set that can represent all of the characters found in all human languages. It is a unification of dozens of character sets, such as Latin, Greek, Arabic, Cyrillic, Hebrew, Katakana, Hangul, and many more. Thus, in Java char is a 16-bit type. The range of a char is 0 to 65,536. There are no negative chars.
- 45. 45 Arvind Bhave DATA TYPES // Demonstrate char data type. class CharDemo { public static void main(String args[]) { char ch1, ch2; ch1 = 88; // code for X ch2 = 'Y'; System.out.print("ch1 and ch2: "); System.out.println(ch1 + " " + ch2); ch1 = 'X'; System.out.println("ch1 contains " + ch1); ch1++; // increment ch1 System.out.println("ch1 is now " + ch1); } }
- 46. 46 Arvind Bhave DATA TYPES Booleans boolean, for logical values. It can have only one of two possible values, true or false. This is the type returned by all relational operators, such as a < b. boolean is also the type required by the conditional expressions that govern the control statements such as if and for.
- 47. 47 Arvind Bhave DATA TYPES // Demonstrate boolean values. class BoolTest { public static void main(String args[]) { boolean b; b = false; System.out.println("b is " + b); b = true; System.out.println("b is " + b); // a boolean value can control the if statement if(b) System.out.println("This is executed."); b = false; if(b) System.out.println("This is not executed."); // outcome of a relational operator is a boolean value System.out.println("10 > 9 is " + (10 > 9)); } } The output generated by this program is shown here: b is false b is true This is executed. 10 > 9 is true
- 48. 48 Arvind Bhave VARIABLES The variable is the basic unit of storage A variable is defined by the combination of an identifier, a type, and an optional initializer. All variables have a scope, which defines their visibility, and a lifetime. Declaring a Variable In Java, all variables must be declared before they can be used. The basic form of a variable declaration type identifier [ = value][, identifier [= value] ...] ; The type is one of Java’s atomic types, or the name of a class or interface The identifier is the name of the variable
- 49. 49 Arvind Bhave VARIABLES int a, b, c; // declares three ints, a, b, and c. int d = 3, e, f = 5; // declares three more ints, initializing d and f. byte z = 22; // initializes z. double pi = 3.14159; // declares an approximation of pi. char x = 'x'; // the variable x has the value 'x'.
- 50. 50 Arvind Bhave DYNAMIC INITIALIZATION Java allows variables to be initialized dynamically, using any expression valid at the time the variable is declared. For example, here is a short program that computes the length of the hypotenuse of a right triangle given the lengths of its two opposing sides: // Demonstrate dynamic initialization. class DynInit { public static void main(String args[]) { double a = 3.0, b = 4.0; // c is dynamically initialized double c = Math.sqrt(a * a + b * b); System.out.println("Hypotenuse is " + c); } } Here, three local variables—a, b,and c—are declared. The first two, a and b, are initialized by constants. However, c is initialized dynamically to the length of the hypotenuse (using the Pythagorean theorem).
- 51. 51 Arvind Bhave THE SCOPE AND LIFETIME OF VARIABLES Java allows variables to be declared within any block A block is begun with an opening curly brace and ended by a closing curly brace. A block defines a scope. Thus, each time you start a new block, you are creating a new scope. // Demonstrate block scope. class Scope { public static void main(String args[]) { int x; // known to all code within main x = 10; if(x == 10) { // start new scope int y = 20; // known only to this block // x and y both known here. System.out.println("x and y: " + x + " " + y); x = y * 2; } // y = 100; // Error! y not known here // x is still known here. System.out.println("x is " + x); } }
- 52. 52 Arvind Bhave LIFETIME OF A VARIABLE. // Demonstrate lifetime of a variable. class LifeTime { public static void main(String args[]) { int x; for(x = 0; x < 3; x++) { int y = -1; // y is initialized each time block is entered System.out.println("y is: " + y); // this always prints -1 y = 100; System.out.println("y is now: " + y); } } } The output generated by this program is shown here: y is: -1 y is now: 100 y is: -1 y is now: 100 y is: -1 y is now: 100
- 53. 53 Arvind Bhave TYPE CONVERSION AND CASTING If the two types are compatible, then Java will perform the conversion automatically. For example, it is always possible to assign an int value to a long variable. However, not all types are compatible, and thus, not all type conversions are implicitly allowed. For instance, there is no conversion defined from double to byte. Fortunately, it is still possible to obtain a conversion between incompatible types. To do so, you must use a cast, which performs an explicit conversion between incompatible types.
- 54. 54 Arvind Bhave JAVA’S AUTOMATIC CONVERSIONS When one type of data is assigned to another type of variable, an automatic type conversion will take place if the following two conditions are met: ■ The two types are compatible. ■ The destination type is larger than the source type. When these two conditions are met, a widening conversion takes place. For example, the int type is always large enough to hold all valid byte values, so no explicit cast statement is required.
- 55. 55 Arvind Bhave CASTING INCOMPATIBLE TYPES Although the automatic type conversions are helpful, they will not fulfill all needs. For example, what if you want to assign an int value to a byte variable? This conversion will not be performed automatically, because a byte is smaller than an int. This kind of conversion is sometimes called a narrowing conversion, since you are explicitly making the value narrower so that it will fit into the target type.
- 56. 56 Arvind Bhave CASTING INCOMPATIBLE TYPES To create a conversion between two incompatible types, you must use a cast. A cast is simply an explicit type conversion. It has this general form: (target-type) value Here, target-type specifies the desired type to convert the specified value to. For example, the following fragment casts an int to a byte. If the integer’s value is larger than the range of a byte, it will be reduced modulo (the remainder of an integer division by the) byte’s range
- 57. 57 Arvind Bhave CASTING INCOMPATIBLE TYPES int a; byte b; // ... b = (byte) a; A different type of conversion will occur when a floating-point value is assigned to an integer type: truncation. As you know, integers do not have fractional components. Thus, when a floating-point value is assigned to an integer type, the fractional component is lost. For example, if the value 1.23 is assigned to an integer, the resulting value will simply be 1. The 0.23 will have been truncated. Of course, if the size of the whole number component is too large to fit into the target integer type, then that value will be reduced modulo the target type’s range.
- 58. 58 Arvind Bhave CASTING INCOMPATIBLE TYPES The following program demonstrates some type conversions that require casts: // Demonstrate casts. class Conversion { public static void main(String args[]) { byte b; int i = 257; double d = 323.142; System.out.println("nConversion of int to byte."); b = (byte) i; System.out.println("i and b " + i + " " + b); System.out.println("nConversion of double to int."); i = (int) d; System.out.println("d and i " + d + " " + i); System.out.println("nConversion of double to byte."); b = (byte) d; System.out.println("d and b " + d + " " + b); } }
- 59. 59 Arvind Bhave CASTING INCOMPATIBLE TYPES Output Conversion of int to byte. i and b 257 1 Conversion of double to int. d and i 323.142 323 Conversion of double to byte. d and b 323.142 67 When the value 257 is cast into a byte variable, the result is the remainder of the division of 257 by 256 (the range of a byte), which is 1 in this case. When the d is converted to an int, its fractional component is lost. When d is converted to a byte, its fractional component is lost, and the value is reduced modulo 256, which in this case is 67.
- 60. 60 Arvind Bhave AUTOMATIC TYPE PROMOTION IN EXPRESSIONS byte a = 40; byte b = 50; byte c = 100; int d = a * b / c; The result of the intermediate term a * b easily exceeds the range of either of its byte operands. To handle this kind of problem, Java automatically promotes each byte or short operand to int when evaluating an expression. This means that the sub expression a * b is performed using integers—not bytes. Thus, 2,000, the result of the intermediate expression, 50 * 40, is legal even though a and b are both specified as type byte.
- 61. 61 Arvind Bhave AUTOMATIC TYPE PROMOTION IN EXPRESSIONS As useful as the automatic promotions are, they can cause confusing compile-time errors. For example, this seemingly correct code causes a problem: byte b = 50; b = b * 2; // Error! Cannot assign an int to a byte!
- 62. 62 Arvind Bhave AUTOMATIC TYPE PROMOTION IN EXPRESSIONS The code is attempting to store 50 * 2, a perfectly valid byte value, back into a byte variable. However, because the operands were automatically promoted to int when the expression was evaluated, the result has also been promoted to int. Thus, the result of the expression is now of type int, which cannot be assigned to a byte without the use of a cast. This is true even if, as in this particular case, the value being assigned would still fit in the target type. In cases where you understand the consequences of overflow, you should use an explicit cast, such as byte b = 50; b = (byte)(b * 2); which yields the correct value of 100.
- 63. 63 Arvind Bhave THE TYPE PROMOTION RULES Java defines several type promotion rules that apply to expressions. They are as follows. First, all byte and short values are promoted to int, as just described. Then, if one operand is a long, the whole expression is promoted to long. If one operand is a float, the entire expression is promoted to float. If any of the operands is double, the result is double.
- 64. 64 Arvind Bhave THE TYPE PROMOTION RULES The following program demonstrates how each value in the expression gets promoted to match the second argument to each binary operator: class Promote { public static void main(String args[]) { byte b = 42; char c = 'a'; short s = 1024; int i = 50000; float f = 5.67f; double d = .1234; double result = (f * b) + (i / c) - (d * s); System.out.println((f * b) + " + " + (i / c) + " - " + (d * s)); System.out.println("result = " + result); } }
- 65. 65 Arvind Bhave Let’s look closely at the type promotions that occur in this line from the program: double result = (f * b) + (i / c) - (d * s); In the first subexpression, f * b, b is promoted to a float and the result of the sub expression is float. Next, in the sub expression i / c, c is promoted to int, and the result is of type int. Then, in d * s, the value of s is promoted to double, and the type of the subexpression is double. Finally, these three intermediate values, float, int, and double, are considered. The outcome of float plus an int is a float. Then the resultant float minus the last double is promoted to double, which is the type for the final result of the expression.
- 66. 66 Arvind Bhave ARRAYS An array is a group of like-typed variables that are referred to by a common name. Arrays of any type can be created and may have one or more dimensions. A specific element in an array is accessed by its index
- 67. 67 Arvind Bhave ONE-DIMENSIONAL ARRAYS A one-dimensional array is, essentially, a list of like-typed variables.. The general form of a one dimensional array declaration is type var-name[ ]; Here, type declares the base type of the array. The base type determines the data type of each element that comprises the array. For example, the following declares an array named month_days with the type “array of int”: int month_days[]; Although this declaration establishes the fact that month_days is an array variable, no array actually exists. In fact, the value of month_days is set to null, which represents an array with no value.
- 68. 68 Arvind Bhave ONE-DIMENSIONAL ARRAYS To link month_days with an actual, physical array of integers, you must allocate one using new and assign it to month_days. new is a special operator that allocates memory. The general form of new as it applies to one- dimensional arrays appears as follows: array-var = new type[size]; Here, type specifies the type of data being allocated, size specifies the number of elements in the array, and array-var is the array variable that is linked to the array.
- 69. 69 Arvind Bhave ONE-DIMENSIONAL ARRAYS This example allocates a 12-element array of integers and links them to month_days. month_days = new int[12]; After this statement executes, month_days will refer to an array of 12 integers. Further, all elements in the array will be initialized to zero.
- 70. 70 Arvind Bhave ONE-DIMENSIONAL ARRAYS Here is one more example that uses a one-dimensional array. It finds the average of a set of numbers. // Average an array of values. class Average { public static void main(String args[]) { double nums[] = {10.1, 11.2, 12.3, 13.4, 14.5}; double result = 0; int i; for(i=0; i<5; i++) result = result + nums[i]; System.out.println("Average is " + result / 5); } }
- 71. 71 Arvind Bhave MULTIDIMENSIONAL ARRAYS In Java, multidimensional arrays are actually arrays of arrays. These, as you might expect, look and act like regular multidimensional arrays. For example, the following declares a two- dimensional array variable called twoD. int twoD[][] = new int[4][5]; This allocates a 4 by 5 array and assigns it to twoD. Internally this matrix is implemented as an array of arrays of int.
- 72. 72 Arvind Bhave // Demonstrate a two-dimensional array. class TwoDArray { public static void main(String args[]) { int twoD[][]= new int[4][5]; int i, j, k = 0; for(i=0; i<4; i++) for(j=0; j<5; j++) { twoD[i][j] = k; k++; } for(i=0; i<4; i++) { for(j=0; j<5; j++) System.out.print(twoD[i][j] + " "); System.out.println(); } } }
- 73. 73 Arvind Bhave This program generates the following output: 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
- 74. 74 Arvind Bhave 2 D ARRAY It is possible to initialize multidimensional arrays. Enclose each dimension’s initializer within its own set of curly braces. Initialization of 2 D Array double m[][] = { { 0*0, 1*0, 2*0, 3*0 }, { 0*1, 1*1, 2*1, 3*1 }, { 0*2, 1*2, 2*2, 3*2 }, { 0*3, 1*3, 2*3, 3*3 } }; 0*0=column*row
- 75. 75 Arvind Bhave ALTERNATIVE ARRAY DECLARATION SYNTAX There is a second form that may be used to declare an array: type[ ] var-name; Here, the square brackets follow the type specifier, and not the name of the array variable. For ex, the following two declarations are equivalent: int al[] = new int[3]; int[] a2 = new int[3]; The following declarations are also equivalent: char ch1[][] = new char[3][4]; char[][] ch2 = new char[3][4];
- 76. 76 Arvind Bhave STRING TYPE Java’s string type, called String, is not a simple type. Nor is it simply an array of characters (as are strings in C/C++). Rather, String defines an object, and a full description of it requires an understanding of several object-related features. The String type is used to declare string variables. You can also declare arrays of strings. A quoted string constant can be assigned to a String variable.
- 77. 77 Arvind Bhave A variable of type String can be assigned to another variable of type String. You can use an object of type String as an argument to println( ). For example, consider the following fragment: String str = "this is a test"; System.out.println(str); Here, str is an object of type String. It is assigned the string “this is a test”. This string is displayed by the println( ) statement.
- 78. 78 Arvind Bhave ARITHMETIC OPERATORS Arithmetic operators are used in mathematical expressions in the same way that they are used in algebra. The following table lists the arithmetic operators: + Addition – Subtraction (also unary minus) * Multiplication / Division % Modulus ++ Increment += Addition assignment –= Subtraction assignment *= Multiplication assignment /= Division assignment %= Modulus assignment – – Decrement
- 79. 79 Arvind Bhave RELATIONAL OPERATORS The relational operators determine the relationship that one operand has to the other. Specifically, they determine equality and ordering. The relational operators are shown here: == Equal to != Not equal to > Greater than < Less than >= Greater than or equal to <= Less than or equal to The outcome of these operations is a boolean value
- 80. 80 Arvind Bhave BOOLEAN LOGICAL OPERATORS The Boolean logical operators shown here operate only on boolean operands. All of the binary logical operators combine two boolean values to form a resultant boolean value. & Logical AND | Logical OR ^ Logical XOR (exclusive OR) || Short-circuit OR && Short-circuit AND ! Logical unary NOT &= AND assignment |= OR assignment ^= XOR assignment == Equal to != Not equal to ?: Ternary if-then-else
- 81. 81 Arvind Bhave A B A | B A & B A ^ B !A False False False False False True True False True False True False False True True False True True True True True True False False
- 82. 82 Arvind Bhave CONTROL STATEMENTS If If-else Nested ifs if(i == 10) { if(j < 20) a = b; if(k > 100) c = d; // this if is else a = c; // associated with this else } else a = d; // this else refers to if(i == 10)
- 83. 83 Arvind Bhave The if-else-if Ladder if(condition) statement; else if(condition) statement; else if(condition) statement; ... else statement;
- 84. 84 Arvind Bhave The if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the ladder is bypassed. If none of the conditions is true, then the final else statement will be executed.
- 85. 85 Arvind Bhave // Demonstrate if-else-if statements. class IfElse { public static void main(String args[]) { int month = 4; // April String season; if(month == 12 || month == 1 || month == 2) season = "Winter"; else if(month == 3 || month == 4 || month == 5) season = "Spring"; else if(month == 6 || month == 7 || month == 8) season = "Summer"; else if(month == 9 || month == 10 || month == 11) season = "Autumn"; else season = "Bogus Month"; System.out.println("April is in the " + season + "."); } }
- 86. 86 Arvind Bhave SWITCH The switch statement is Java’s multiway branch statement. switch (expression) { case value1: // statement sequence break; case value2: // statement sequence break; ... case valueN: // statement sequence break; default: // default statement sequence }
- 87. 87 Arvind Bhave A simple example of the switch. class SampleSwitch { public static void main(String args[]) { for(int i=0; i<6; i++) switch(i) { case 0: System.out.println("i is zero."); break; case 1: System.out.println("i is one."); break; case 2: System.out.println("i is two."); break; case 3: System.out.println("i is three."); break; default: System.out.println("i is greater than 3."); } } }