Variables
[ data_type ] variable_name;
[ data_type ] variable_name = initial_value;
int num = 5;
double value;
value = 22.4;
|
If Statement
if ( condition ) {
statements
} else if ( condition ) {
statements
} else {
statements
}
|
Switch Statement
switch ( condition ) {
case value:
statements
break;
case value2:
statements
break;
default:
statements
break;
}
|
For loop
for ( initialize ; condition ; increment ) {
statements
}
|
While Loop
while ( condition ) {
statements
}
|
Do-While Loop
do {
statements
} while ( condition );
|
1D Arrays
element_type[] variable_name;
element_type[] variable_name = new element_type [ array_size ] ;
element_type[] variable_name = { value1, value2, value3, ... };
element_type name = variable_name [ index ];
variable_name [ index ] = value;
// example
int[] arr = new int[10];
double[] nums = {22.1, 50, 34};
int a = arr[0];
arr[0] = 53;
// iteration, full array, from start to end
for (int i = 0; i < arr.length; i++) {
int element = arr[i];
}
|
Methods
[modifiers] return-type name ( parameters ) {
statements
}
// modifiers
[ access-modifier ] [ static / abstract ] [ synchronized ] [ final ]
// examples
public static void printName() {
statements
}
public void showNumbers(int a, int b) {
statements
}
public int sum(int a, int b) {
return a + b;
}
|
Main
public static void main(String[] args) {
}
|
Class Structure
public class name {
members
constructors
methods
}
public class name {
private type var1;
private type var2;
public name ( type var1, type var2) {
this.var1 = var1;
this.var2 = var2;
}
public return_type method1 ( type param1, type param2 ) {
statements
}
public return_type method2 ( params ) {
statements
}
}
|
|
|
Primitive Data Types
byte |
integers |
1 byte |
short |
integers |
2 bytes |
int |
integers |
4 bytes |
long |
integers |
8 bytes |
float |
decimals |
4 bytes |
double |
decimals |
8 bytes |
char |
characters |
2 bytes |
boolean |
boolean |
1 bytes |
Arithmetic Operators
num1 + num2 |
addition |
num1 - num2 |
subtraction |
num1 * num2 |
multiplication |
num1 / num2 |
division |
num1 % num2 |
modulus |
num++ |
post increment |
num-- |
post decrement |
++num |
pre increment |
--num |
pre decrement |
Assignment Operators
num1 = value |
|
assignment |
num1 += num2 |
num1 = num1 + num2 |
addition |
num1 -= num2 |
num1 = num1 - num2 |
subtraction |
num1 *= num2 |
num1 = num1 * num2 |
multiplication |
num1 /= num2 |
num1 = num1 / num2 |
division |
num1 %= num2 |
num1 = num1 % num2 |
modulus |
Comparison Operators
num1 == num2 |
Equal To |
num1 != num2 |
Not Equal |
num1 > num2 |
Greater Than |
num1 < num2 |
Less Than |
num1 >= num2 |
Greater Than or Equal to |
num1 <= num2 |
Less Than or Equal to |
Logical Operators
boolean1 && boolean2 |
Logical AND |
boolean1 || boolean2 |
Logical OR |
! boolean1 |
Logical NOT |
Binary Operators
num1 | num2 |
Bitwise OR |
num1 & num2 |
Bitwise AND |
num1 ^ num2 |
Bitwise XOR |
~num1 |
Bitwise Complement |
num1 >> num2 |
Right Shift |
num1 << num2 |
Left Shift |
num1 >>> num2 |
Unsigned Right Shift |
Type Conversion
// type casting
double val = 25.2;
int a = (int) val; // will be 25
// to string conversion
int number = 24;
String str = String.valueOf(number);
// or with string concat: "hello: " + number
// string to int
String str = "25";
int val = Integer.parseInt(str);
// string to double
String str = "25.5";
double val = Double.parseDouble(str);
|
Literals
// integers
int num1 = 34; // base 10 (decimal)
int num2 = 042; // base 8 (octal)
int num3 = 0x22; // base 16 (hexadecimal)
int num4 = 0b00100010; // base 2 (binary)
long value = 2211153122345L;
// decimals
float value = 155.4f;
double value = 155.4;
double value = 1.554e2; // exponent form
// char, String
char a = 'A';
char a = '\u0021';
char a = 67;
String b = "Hello World";
|
Access Modifiers
public |
Any code |
private |
Only code in the same class |
protected |
Only code in the same class, inheriting class or the same package |
package-private (default, set no modifier) |
Only code in the same package |
Modifiers
final |
Cannot be overriden or extended |
static |
Belongs to the class, rather than an instance |
abstract (on method) |
Declares the method as abstract, requiring no body |
abstract (on class) |
Declares the class as abstract, can contain abstract methods |
synchronized |
Holds monitor on class instance during method execution |
transient |
Attributes and methods are skipped when serializing the object containing them (via java object serialization) |
volatile |
The value of the attribute is not cached on CPU |
Math Methods
// basic
double pi = Math.PI; // pi
double val = Math.abs(-15); // 15, absolute value
double val = Math.signum(-15); // -1, sign (-1, 0, 1)
double val = Math.max(12, 13); // 13, max of 2 numbers
double val = Math.min(12, 13); // 12, min of 2 numbers
double val = Math.sqrt(16); // square root of number
double val = Math.pow(2, 4); // 2 to the power of 4
// round
double val = Math.ceil(15.2); // 16, round up
double val = Math.floor(15.2); // 15, round down
double val = Math.round(15.2); // 15, round to the closest
// trigo
double degrees = Math.toDegrees(Math.PI); // radians to degrees
double radians = Math.toRadians(180); // degrees to radians
double val = Math.sin(radians); // sine func
double val = Math.cos(radians); // cosine func
double val = Math.tan(radians); // tangent func
double radians = Math.asin(value); // arc sine func
double radians = Math.acos(value); // arc cosine func
double radians = Math.atan(value); // arc tangent func
|
Method Invocation
method_name();
method_name( parameters );
return_type name = method_name( parameters );
printName();
int sum = sumNumbers(11, 90);
|
Objects
// creation
Class_Name var_name;
Class_Name var_name = new Class_Name();
Class_Name var_name = new Class_Name( parameters );
Person person;
Person person = new Person("Barak Obama", 25);
// access
type name = var_name.attribute;
var_name.attribute = value;
int a = person.age;
person.age = 55;
// method invocation
var_name.method_name();
var_name.method_name( parameters );
return_type name = var_name.method_name( parameters );
String name = person.getName();
person.walkDistance(5);
|
|
