An array is a container object that holds a fixed number of values of a single type. The length of an array is established when the array is created. After creation, its length is fixed.

int[] numbers = new int[3];  // Creates space for 3 integers
numbers[0] = 10;
numbers[1] = 20;
numbers[2] = 30;

System.out.println(numbers[1]);  // Output: 20

Declaring and Initializing Arrays

There are two main ways:

1. Declare and assign later: 

int[] marks;
marks = new int[5];

2. Declare and initialize in one step: 

int[] marks = {90, 80, 70, 60, 50};

Looping Through Arrays

Use a loop to print all elements:

for (int i = 0; i < marks.length; i++) {
    System.out.println(marks[i]);
}

Or use an enhanced for-loop:

for (int mark : marks) {
    System.out.println(mark);
}

Common Array Types

You can create arrays of any data type:

String[] names;
double[] prices;
boolean[] flags;

Multidimensional Arrays

Arrays inside arrays (like a table):

String[][] names = {
    {"Mr. ", "Ms. "},
    {"Smith", "Jones"}
};

System.out.println(names[0][0] + names[1][0]);  // Output: Mr. Smith

Copying Arrays

Manual way: 

int[] source = {1, 2, 3};
int[] target = new int[3];

for (int i = 0; i < source.length; i++) {
    target[i] = source[i];
}

Using System.arraycopy(): 

System.arraycopy(source, 0, target, 0, source.length);

Using Arrays.copyOf(): 

int[] target = java.util.Arrays.copyOf(source, source.length);

Helpful Methods in java.util.Arrays 

import java.util.Arrays;

Arrays.sort(marks);               // Sort the array
int pos = Arrays.binarySearch(marks, 70);  // Search
boolean same = Arrays.equals(marks, target); // Compare
Arrays.fill(marks, 100);          // Fill with same value
System.out.println(Arrays.toString(marks)); // Print nicely

Summary


Classes
Quiz
Videos
References
Books