Java: Arrays

By Xah Lee. Date: . Last updated: .

This page shows how to create array in Java.

Array in Java is like a fixed number of slots, each slot holds a item, and all of them the same type.

Here's a example.

/* example showing array declaration, initialization, and filling out the slots. */
public class Ar {
    public static void main(String[] args) {

        // declare var that's array of int datatype
        int[] myA;

        // assign the array int items, 10 of them
        myA = new int[10];

        // array assignment for each slot is like this:
        myA[3] = 7;
        System.out.print(myA[3] + "\n"); // prints 7

        // myA.length returns number of items
        System.out.print(myA.length + "\n"); // prints 10

        // if a array slot has not given a value, it is garbage.
        // In this specific case, java fills it with 0.
        for (int i = 0; i < myA.length; i++) {
            System.out.print(myA[i] + " ");
        } // prints 0 0 0 7 0 0 0 0 0 0
    }
}

Things to remember:

Note that code like int[10] myArray; is illegal.

Assign Array Slots Shortcut

You can use this shortcut syntax int[] myArray = {3,7,4}; to declare and initialize array at the same time

// example of array
public class Aj {
    public static void main(String[] args) {
        int[] myA = {3,7,4};
        for (int i = 0; i < myA.length; i++) {
            System.out.print(myA[i] + " ");
        } // prints 3 7 4
    }
}

2-Dimensional Arrays

The syntax to declare 2-dimensional array is this type_or_class[][].

public class Ar2 {
    public static void main(String[] args) {

        // declaring that myA is a 2-dimensional array
        int[][] myA;

        // give the variable a value, and declare its dimensions.
        myA = new int[3][2];

        // assign a value to a array slot
        myA[0][0] = 6;

        System.out.print(myA[0][0]); // prints the value of a slot
        System.out.println();
        System.out.print(myA[0].length); // prints the length of a row
    }
}

Note: list-like things such as lists, hash table, see Java: Collection, Map.

Jagged Arrays

You can create a 2D array with m rows and each row have different number of slots.

Java: Jagged Arrays

Array of Objects

Array element can be any object.

See: Java: Array of Objects.

Resizable Array

Array cannot be resized (cannot add element).

If you want to be able to resize array, use ArrayList. See: Java: Collection, Map

Java

  1. Install
  2. javac java jar javadoc

Java Basics

  1. Print String
  2. Strings
  3. Power Function
  4. Java Types and Type Conversion
  5. Function
  6. Arrays

Class, Inheritance

  1. extends
  2. Constructor
  3. Constructor Return Type
  4. Extending a Class that has Explicit Constructors
  5. static
  6. this
  7. super
  8. Access Specifiers

Abstract class, Interface

  1. abstract
  2. Interface

Package

  1. Package

Misc

  1. Collection, Map
  2. Read/Write File
  3. Convert File Encoding
  4. Complex Numbers in Java
  5. Unicode
  6. Number Literals