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Quick Java Tutorial

Learn the basics of Java programming. Covering variables, conditionals, loops, methods, classes, and objects.

Overview

On this page we will cover

Variables

/* Syntax: Type variableName = VALUE; */
int wholeNumber = 93;
double numberWithDigits = 46.85;
String text = "words and stuff";
boolean isValid = true;
boolean isNegative = -3 < 0;
MyObject obj = new MyObject();

Conditionals

if (boolean1) {
// if boolean1 is true
} else if (boolean2) {
// if boolean1 is false but boolean2 is true
} else {
// if boolean1 and boolean2 were both false
}

Loops

while (isLoopActive) {
// keep doing something
}
// isLoopActive became false
for (int i = 0; i < 5; i++) { // start with i=0, increment i each time, continue while i < 5
// do something 5 times
}

Class Methods

/* Syntax: keywords returnType methodName(ParameterType parameterName, ...) { */
public static final double divide(int dividend, double divisor) {
double quotient = dividend / divisor;
return quotient;
}
private void moveForward(double inches) {
// code to move forward [inches] inches
// don't need to return, as returnType is 'void'
}
public abstract void overrideMeLater;
Keywords:
Access Modifier keyword
Description
public
Method is accessible by any class
private
Method is accessible by the same class
protected
Method is accessible by the same class and any subclasses
[leave blank]
Method is accessible only by the class's object
Non-Access Modifier keyword
Description
static
Method belongs to class [Class.call()], not the object [object.call()]
abstract
Method must be overridden and does not have a body
final
Method cannot be overridden

Classes

public class ClassName {
// class variables here
String name;
// constructor
public ClassName() {
this("default name");
}
public ClassName(String name) {
this.name = name;
}
// class methods here
public String getName() {
return name;
}
}

Using Objects

// Creating objects
MyObject objName1 = new MyObject();
MyObject objName2 = new MyObject("Second try");
// Calling methods
MyObject.staticMethod();
objName1.method();
objName2.method();
// Using return values
String output = objName1.toString() + " | " + objName2.toString();
// Note: objects are just unique instances of a class;
// you can have multiple of the same class