Java Cheat Sheet
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This document provides a comprehensive Java cheat sheet covering data types, control statements, exception handling, data conversions, string methods, ArrayList and HashMap methods, operators, and text formatting. It includes practical code examples along with syntax for Java programming. The document serves as a quick reference for Java developers.
![Java Cheat Sheet
Java Data Types
byte / short / int /
long
‑123, 10
float / double 235.13
char 'U'
boolean true, false
String "Greetings from
earth"
Java Statements
If Statement
if ( expression ) {
statements
} else if ( expression ) {
statements
} else {
statements
}
While Loop
while ( expression ) {
statements
}
Do‑While Loop
do {
statements
} while ( expression );
For Loop
for ( int i = 0; i < max ; ++i) {
statements
}
For Each Loop
for ( var : collection ) {
statements
}
Switch Statement
switch ( expression ) {
case value :
statements
break;
case value2 :
statements
break;
default:
statements
}
Exception Handling
try {
statements;
} catch (ExceptionType e1 ) {
statements;
} catch (Exception e2 ) {
catch‑all statements;
} finally {
statements;
}
Java Data Conversions
String to Number
int i = Integer.parseInt(str );
double d = Double.parseDouble(str );
Any Type to String
String s = String.valueOf(value );
Numeric Conversions
int i = (int) numeric expression ;
Java String Methods
s .length() length of s
s .charAt(i ) extract i th character
s .substring(start ,
end )
substring from start to
end ‑1
s .toUpperCase() returns copy of s in ALL
CAPS
s .toLowerCase() returns copy of s in
lowercase
s .indexOf(x ) index of first occurence
of x
s .replace(old ,
new )
search and replace
s .split(regex ) splits string into tokens
s .trim() trims surrounding
whitespace
s .equals(s2 ) true if s equals s2
s .compareTo(s2 ) 0 if equal/+ if s > s2/‑
if s < s2
java.util.ArrayList Methods
l .add(itm ) Add itm to list
l .get(i ) Return i th item
l .size() Return number of items
l .remove(i ) Remove i th item
l .set(i , val ) Put val at position i
ArrayList<String> names = new
ArrayList<String>();
java.util.HashMap Methods
m .put(key ,value ) Inserts value with key
m .get(key ) Retrieves value with
key
m .containsKey(key ) true if contains key
HashMap<String,String> names = new
HashMap<String, String>();
Updated by Saeid Zebardast
Twitter: @saeid
Email: saeid.zebardast@gmail.com
Home: http://zebardast.ir
About: http://about.me/saeid
Java Hello World
import java.util.Date;
public class Hello {
public static void main(String[] args) {
System.out.println("Hello, world!");
Date now = new Date();
System.out.println("Time: " + now);
}
}
* Save in Hello.java
* Compile: javac Hello.java
* Run: java Hello
Java Arithmetic Operators
x +
y
add x ‑ y subtract
x *
y
multiply x / y divide
x %
y
modulus ++x /
x++
increment
‑‑x / x‑‑ decrement
Assignment shortcuts: x op = y
Example: x += 1 increments x
Java Comparison Operators
x < y Less x <= y Less or eq
x > y Greater x >= y Greater or eq
x ==
Equal x != y Not equal
y
Java Boolean Operators
! x (not) x && y (and) x || y (or)
Java Text Formatting
printf style formatting
System.out.printf("Count is %dn", count);
s = String.format("Count is %d", count);
MessageFormat style formatting
s = MessageFormat.format(
"At {1,time}, {0} eggs hatched.",
25, new Date());
Individual Numbers and Dates
s = NumberFormat.getCurrencyInstance()
.format(x);
s = new SimpleDateFormat(""h:mm a"")
.format(new Date());
s = new DecimalFormat("#,##0.00")
.format(125.32);
Source: http://cheatography.com/sschaub](https://image.slidesharecdn.com/gksn7oxtbepbzdsodvrg-signature-fd6d5730ec02f85f4d2799a60336af8273582a48cc77d2c81c10bb7f353f1ff1-poli-141213092950-conversion-gate02/85/Java-Cheat-Sheet-1-320.jpg)
Java Cheat Sheet
- 1. Java Cheat Sheet Java Data Types byte / short / int / long ‑123, 10 float / double 235.13 char 'U' boolean true, false String "Greetings from earth" Java Statements If Statement if ( expression ) { statements } else if ( expression ) { statements } else { statements } While Loop while ( expression ) { statements } Do‑While Loop do { statements } while ( expression ); For Loop for ( int i = 0; i < max ; ++i) { statements } For Each Loop for ( var : collection ) { statements } Switch Statement switch ( expression ) { case value : statements break; case value2 : statements break; default: statements } Exception Handling try { statements; } catch (ExceptionType e1 ) { statements; } catch (Exception e2 ) { catch‑all statements; } finally { statements; } Java Data Conversions String to Number int i = Integer.parseInt(str ); double d = Double.parseDouble(str ); Any Type to String String s = String.valueOf(value ); Numeric Conversions int i = (int) numeric expression ; Java String Methods s .length() length of s s .charAt(i ) extract i th character s .substring(start , end ) substring from start to end ‑1 s .toUpperCase() returns copy of s in ALL CAPS s .toLowerCase() returns copy of s in lowercase s .indexOf(x ) index of first occurence of x s .replace(old , new ) search and replace s .split(regex ) splits string into tokens s .trim() trims surrounding whitespace s .equals(s2 ) true if s equals s2 s .compareTo(s2 ) 0 if equal/+ if s > s2/‑ if s < s2 java.util.ArrayList Methods l .add(itm ) Add itm to list l .get(i ) Return i th item l .size() Return number of items l .remove(i ) Remove i th item l .set(i , val ) Put val at position i ArrayList<String> names = new ArrayList<String>(); java.util.HashMap Methods m .put(key ,value ) Inserts value with key m .get(key ) Retrieves value with key m .containsKey(key ) true if contains key HashMap<String,String> names = new HashMap<String, String>(); Updated by Saeid Zebardast Twitter: @saeid Email: [email protected] Home: http://zebardast.ir About: http://about.me/saeid Java Hello World import java.util.Date; public class Hello { public static void main(String[] args) { System.out.println("Hello, world!"); Date now = new Date(); System.out.println("Time: " + now); } } * Save in Hello.java * Compile: javac Hello.java * Run: java Hello Java Arithmetic Operators x + y add x ‑ y subtract x * y multiply x / y divide x % y modulus ++x / x++ increment ‑‑x / x‑‑ decrement Assignment shortcuts: x op = y Example: x += 1 increments x Java Comparison Operators x < y Less x <= y Less or eq x > y Greater x >= y Greater or eq x == Equal x != y Not equal y Java Boolean Operators ! x (not) x && y (and) x || y (or) Java Text Formatting printf style formatting System.out.printf("Count is %dn", count); s = String.format("Count is %d", count); MessageFormat style formatting s = MessageFormat.format( "At {1,time}, {0} eggs hatched.", 25, new Date()); Individual Numbers and Dates s = NumberFormat.getCurrencyInstance() .format(x); s = new SimpleDateFormat(""h:mm a"") .format(new Date()); s = new DecimalFormat("#,##0.00") .format(125.32); Source: http://cheatography.com/sschaub