Intro to Java Cheat Sheet

Reserved Words

Java Reserved Words
abstract boolean break byte case catch clear class continue default
do double else extends final finally float for if implements
import instanceof int interface long native new package private protected
public return short static strictfp super switch synchronized this throw
throws transient try void volatile while const goto null true
false rest cast generic outer inner future byvalue var

Data Types

Primitives
Type Size (bits) Size (bytes) Values Example
byte 8 bits 1 byte -128 to 127 
byte b = 12;
short 16 bits 2 bytes -32768 to 32767 
short sh = 1000;
int 32 bits 4 bytes -2**31 to 2**31 - 1 
int i = 45900;
long 64 bits 8 bytes 2**63 to 2**63 - 1 
long l = 1000000;
float 32 bits 4 bytes big 
float f = 12.34;
double 64 bits 8 bytes really big 
double d = 1.7e40;
char 16 bits 2 bytes Unicode characters 
char c = 'a';
boolean 8 bits 1 byte true or false 
boolean done = false;

Flow Control Statements

The if Statement

   if ( a < b )
   {
       System.out.println ( a );
   }
   else
   {
       System.out.println ( b );
   }

The for Loop

    for ( int i = 0; i < 10; i++ )
    {
        System.out.println ( i );
    }

The switch-case Statement

    int i = ??????
    switch ( i )
    {
        case 12:
            System.out.println ( "It's twelve!" );
            break;
			
        default:
            System.out.println ( "It's something else!" );
            break;
    }

Using Classes

Defining a Class

Filename: Student.java 
    public class Student extends Object
    {
        private int studentID;
        private String name;
		
        public Student ( int id, String n ) // constructor
        {
            studentID = id;
            name = n;
        }
		
        public String toString()
        {
            return "Name: " + name + " ID: " + studentID;
        }
    }

Using a Class

Filename: TestStudent.java 
    public class TestStudent
    {
        public static void main (String args[])
        {
            Student s = new Student ( 12, "Bill" );

            System.out.println ( s );
        }
    }

Compiling and Running

    javac Student.java
    javac TestStudent.java
    java TestStudent