Quick Reference

Quickly lookup Java basics, and load code examples directly into editor.

Method Basics

The header of the method declares what the method will return (such as an int), the method name (doStuff), and the method's parameters (such as a and b). The method body follows, where you usually need to write code that returns a value at the end.


//method header: methodName(parameters)
static int doStuff(int a, int b){
  //your code here - erase this comment and write your code!
  return 1;
}

Load Method
Syntax note: Every line of code in Java needs to end with a ; or it will be considered part of the next line. Comments are marked with 2 backslashes // and are ignored by the computer.

Variables and Data types

Variables need to be declared with their type before they can be used. You can declare and assign a variable on one line: int num = 5; Load Code


//variable examples
//type varName = value;
 int num = 5;
 boolean alive = true;
 String word = "hello";
 double pi = 3.14159;
 char c = 'c';

Operations Booleans and Logic

Math operations are performed in the standard order. Note that division of integers will round down to nearest integer. The mod % operator returns the remainder after division.


int product = 4 * (1+2) / 2;   //6.
int roughDivision = 8 / 3;   //2
int remainder = 3 % 2;     //1, the remainder of 3/2

booleans are used to store true/false values, such as the results of comparisons:


boolean check = false; //this will store result of comparison
int five = 5;
//the following are all true
check = (five == 5);    //equals
check = (five != 3);   //not equals
check = (five >= 5);  //greater or equals

The logical operator AND && will return true if multiple conditions are all true, and OR || will return true if at least one condition is true.


//these pointless statements will both set check to true
check = (3>2 && 2>1); //AND
check = (3>2 || 1>3); //OR

if else and while

The if statement will execute code only if a condition is true:

if(condition){
    //doSomething
}

Load If Statement
The else statement will execute code if the condition was false. The while statement will repeatedly execute the same code while a condition is true.


public static void controlFlow(int number) {
    //this if/else block will print out 1 statement for any number
    if(number > 10){
        System.out.println("big number");
    }
    else if(number > 5){
        System.out.println("medium number");
    }
    else{
        System.out.println("small number");
    }

    //this loop will print the numbers from 0 to 9
    int i = 0;
    while(i < 10){
        System.out.println(i);
        i = i + 1;
    }

}

Printing and Arrays

Print a newline
System.out.println(""); Load Print Statement
The above prints text and add a newline afterwards. System.out.print prints without a newline, but you can add in spaces " " to separate text.


System.out.println("hello"); //prints with newline 
String word1 = "hello";
String word2 = "world";
System.out.print(word1 + " " + word2); //prints "hello world"

Arrays are used to store multiple items of one data type together. They are declared with the type they will hold and with brackets [].
This code creates an empty 5-cell array:
int[] ar1 = new int[5]; Load Array Code
This shortcut creates an array with numbers 0 to 4:
int[] nums = {0,1,2,3,4}; Load Code
You can use for-loop to print values of array:

for(int i=0; i < nums.length; i=i+1){
    System.out.print(nums[i]+" "); 
}

Load Code

Introduction

Collapse Content Show Content

Interested in learning programming with Java? Get started below for free!

Why Learn Java

While some other languages are a little more flexible, Java may be the most in-demand programming language. It is taught in many colleges and is used in everything from large corporate software projects to all Android apps. It has a structured approach that makes it less useful for small scripts, but that can help avoid errors in large projects. Java is a compiled language, which means the code runs faster on computers, but testing out quick lines of code can take a little longer. However, there are tools that let you try out Java code quickly too.

In short, it makes sense to learn Java if you:

Are going to a college that teaches Java
Want to make Android Apps
Want to program for a big company
Want fast software for large projects
Want strict rules to help prevent errors

For more help picking a language, see The Different Programming Languages. It's a good idea to go through the rest of About Programming before doing this module. When you're ready to do some simple code, click on "Next" below.

Next Node

Comments

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Jul 22, 2:22 AM

hope its not hard
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cont...
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Ethan
Oct 29, 11:21 AM

:P your welcome
fayez
May 7, 9:22 AM

What the fudge is going on why can't I continue
Henry
Jan 20, 8:46 PM

cool
Henry
Jan 20, 8:46 PM

this is so cool
محي الدين محمد
May 8, 2:15 AM

ممتاز لدجة لا يصدّق
Jone Jacob
Jun 13, 1:42 PM

Jewel of India | Indian Restaurant | Now Open Weekend Lunch Buffet | Seattle
4735 University Wy NE, Seattle, WA 98105
+12065235275
Seattle is home to a diverse population, and this diversity

cont...
is reflected in its culinary scene. An Indian Cuisine Restaurant In Seattle WA, serves as a culinary oasis where locals and visitors can enjoy traditional Indian dishes. These restaurants pride themselves on using fresh, high-quality ingredients and authentic spices to create meals that transport you straight to the heart of India.
dale styne
Aug 1, 4:08 AM

Heatwave Product Manufacturers is a leading B2B platform connecting buyers and suppliers in the thermal product industry. Specializing in a

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diverse range of heatwave solutions, we cater to businesses seeking high-quality heating equipment, temperature control systems, and thermal management products.

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