Java Basics - Part1

19Z305OBJECT
ORIENTED
PROGRAMMING
Unit 2

Overview
PART
-
1
• Characteristics
of Java
• Data types,
Variables,
Operators
• Control
Statements,
Arrays
PART
-
2
• Classes
• Methods,
Constructors
• Inheritance
• Abstract class
12/1/2020 Vani Kandhasamy,PSG Tech 2

Characteristics
of Java
 Simple
 Secure
 Portable
 Object-oriented
 Robust
 Multithreaded
 Architecture-neutral
 Interpreted & High performance
 Distributed
 Dynamic

Datatypes,Variables,
Operators
Part 1 – Chapter 3 & 4

DataTypes
 Kinds of values that can be stored and manipulated.
 Java - StronglyTyped Language
 Automatic Widening casting
Boolean: boolean (true or false).
Integers: byte, short, int, long (0, 1, -47)
Floating point numbers: float, double (3.14, 1.0, -2.1)
Characters: char (‘X’, 65)
String: String (“hello”, “example”).

public class Example1 {
public static void main(String[] args) {
int myInt = 9;
double myDouble = myInt; // Automatic casting: int to double
System.out.println(myInt); // Outputs 9
System.out.println(myDouble); // Outputs 9.0
}
}

Variables
 Named location that stores a value of one particular type.
 Syntax: type variable ; (0r) type variable = value;
 Example: String rollNo;
rollNo = “19Z30X”;
(or)
String rollNo = “19Z30X”;

class Example2 {
public static void printSquare(int x){
System.out.println("printSquare x = " + x);
x = x * x;
System.out.println("printSquare x = " + x);
}
public static void main(String[] arguments){
int x = 5;
System.out.println("main x = " + x);
printSquare(x);
System.out.println("main x = " + x);
}
}

Practice1
Open repl.it
Debug me!!!

Operators
 Symbols that perform simple computations
 Type Promotion
 Syntax: var = var op expression; (or) var op= expression;
Arithmetic operators: (+, -, *, /, …)
Assignment operators: (=, +=, -=,…)
Relational operators: (==, !=, >, <, …)
Logical operators: (&&, ||, !)
Bitwise operators: (&, |, ~, …)

class Example3 {
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);
}
}
Output:
238.14 + 515 - 126.3616
result = 626.7784146484375

Practice2
Open repl.it
Compute distance light travels

ControlStatements,
Arrays
Part 1 – Chapter 3 & 5

Conditional Statements
if (CONDITION) {
STATEMENTS
}
if (CONDITION) {
STATEMENTS
} else {
STATEMENTS
}
if (CONDITION) {
STATEMENTS
} else if (CONDITION) {
STATEMENTS
} else {
STATEMENTS
}

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";
season = "Summer";
season = "Autumn";
else
season = "Bogus Month";
System.out.println("April is in the " + season + ".");
}
}

Selection
Statement
switch (expression) {
case value1:
// statement sequence
break;
case value2:
break;
...
case valueN :
break;
default:
// default statement sequence
}

String str = "two";
switch(str) {
case "one":
System.out.println("one");
break;
case "two":
System.out.println("two");
break;
case "three":
System.out.println("three");
break;
default:
System.out.println("no match");
break;
}
}
}

Overview

Practice3
Open repl.it
Identify season using switch

2
min
Stretch
Break

What if you want to do it for 200 Rules?

Iterative Statements
while (CONDITION) {
STATEMENTS
}
do {
STATEMENTS
} while (CONDITION);
for(initialization;CONDITION;update){
STATEMENTS
}

while

for

S

r

int a, b;
for(a=1, b=4; a<b; a++, b--) {
System.out.println("a = " + a);
System.out.println("b = " + b);
}
}
}

Practice4
Open repl.it
Find whether a number is Prime or
not

Overview

Arrays
Syntax: type var_name[ ] = new type [size];
type[ ] var_name;
Example:
double values[ ] = new double [10]
The index starts at zero and ends at length-1

Declaration &
Instantiation
Initialization
Declaration, Instantiation &
Initialization

int nums[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
int sum = 0;
for(int x =0; x<nums.length; x++){
System.out.println("Value is: " + x);
sum += nums[x];
}
System.out.println("Summation: " + sum);
}
}

int nums[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
int sum = 0;
// use for-each style for to display and sum the values
for(int x : nums) {
System.out.println("Value is: " + x);
sum += x;
}
System.out.println("Summation: " + sum);
}
}

Practice5
Open repl.it
Search an array using for-each style

Multi-
dimensional
Array
int twoD[][] = new int [4][5]
int[][] twoD= new int [4][5]
int []twoD[] = new int [4][5]

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();
}
}
}

Practice6
Open repl.it
Sum of principle diagonal elements
of a matrix

References
 "Java:The Complete Reference” by Schildt H - Part 1 - Chapter 3 , 4 & 5
 https://www.w3schools.com/java/

Java Basics - Part1

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