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

Your First Program

Collapse Content Show Content

Now we will do the same simple problem by coding it. You are again given two variables a and b. You will need to add them together again, but you will also have to return their sum.

To return something, just type return. For example, to return the number 102, you can just type return 102;. Here are some more examples:

return a;
return 5 - 3;
return b + 11;

Instructions

Complete the code below so it returns the sum of a and b.
When you think its correct, click on "Submit" at the bottom to run the code.

The Code

In each programming challenge, you will be given a task. You will be provided with code and need to focus on the part that looks like this:

public static int doStuff(int a, int b){
    //your code here
}

(int a, int b) means you are given two integers a and b as input. You should replace the entire line //your code here with your own code (// marks a comment in code.) Make sure you return something with the keyword return.

Note: In Java, ordinary lines of code need to end with a semi-colon ; so remember to put one at the end of your line of code.

Input/Output Details

In these programming challenge, your code will automatically run on different "test cases" or sets of numbers. You need to return the correct output for each given input of a and b.

You can view some of the input and correct output in the table below, and can compare your results with the correct ones.

Challenge

You are given two variables a and b as input. Can you return the sum of a and b?

(For example, if a is 2 and b is 3, your program should return 5.)

Please sign in or sign up to submit answers.

Alternatively, you can try out Learneroo before signing up.

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Comments

Jarek James
Mar 14, 11:53 AM

This bit is rather scary after you finish reading the whole thing. It is however very simple.
Amos
Mar 20, 6:12 PM

It looks very hard and difficult but just you wait and see when you apply it
Anesi
Jun 13, 6:57 PM

Cool
Adhurim Esati
Jul 1, 5:53 AM

correct me if i'm wrong
"return" has no mathematical function. It is to like "return 5+5" to return the sum of 5+5 to the screen so when the program runs it shows the sum of 5+5 ?
I know I'm not clear but if someone understands pls reply :P
Learneroo
Jul 1, 7:03 PM

return is used in a method to return a value to the code that called it (see next page). This is similar to how a mathematical function returns a value.
Alger
Jul 14, 8:54 AM

It will be easy if you read the article carefully
Mark Herbert
Sep 3, 12:43 PM

its not as complicated as it looks
Patrick
Dec 19, 2:25 PM

I read quick help

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