Declare and initialize two-dimensional arrays in Java
This post will discuss how to declare and initialize two-dimensional arrays in Java.
There are several ways to declare and initialize two-dimensional arrays in Java, which are arrays of arrays that can store data in a tabular form. Here are some possible methods:
1. Using array initializer
We can use the curly braces {} to declare and initialize a two-dimensional array with the values we want. We can use nested braces to specify the rows and columns of the array. For example:
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import java.util.Arrays; public class Main { public static void main(String[] args) { // declare and initialize a 2D array of integers int[][] arr = { {1, 2, 3}, {4, 3, 6}, {7, 8, 9} }; // [[1, 2, 3], [4, 3, 6], [7, 8, 9]] System.out.println(Arrays.deepToString(arr)); } } |
We can also initialize columns of different length with an array initializer. This will result in jagged array, which is an array whose elements are arrays of different dimensions and sizes. For example, the following code declare and initialize a 2D array with different sizes for each row.
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import java.util.Arrays; public class Main { public static void main(String[] args) { // declare and initialize a ragged array of integers int[][] arr = { { 1 }, { 1, 2 }, { 1, 2, 3 } }; // [[1], [1, 2], [1, 2, 3]] System.out.println(Arrays.deepToString(arr)); } } |
2. Using new operator
We can also use the new operator to declare and initialize a two-dimensional array with a specified size. We can assign the dimension of the array using the index notation [row][column]. We can either seperate the declaration and initialization of two-dimensional arrays or combine them in a single line. For example:
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import java.util.Arrays; public class Main { public static void main(String[] args) { int[][] arr1; // declare array arr1 = new int[3][4]; // allocate memory // [[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]] System.out.println(Arrays.deepToString(arr1)); // combine both in a single line int[][] arr2 = new int[3][4]; // [[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]] System.out.println(Arrays.deepToString(arr2)); } } |
Since we have not provided any initializer, the default value of 0 is assigned to each element in the case of int or long or short or byte array. The default value is null for strings, and 0.0 for double or float. Note that the second dimension in a two-dimensional array is optional. We can declare a two-dimensional array by only specifying the first dimension. However, we must specify the first dimension, otherwise the compiler will throw a compilation error.
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import java.util.Arrays; public class Main { public static void main(String[] args) { int[][] arr1 = new int[3][]; arr1[0] = new int[1]; arr1[1] = new int[2]; arr1[2] = new int[3]; // [[0], [0, 0], [0, 0, 0]] System.out.println(Arrays.deepToString(arr1)); int[][] arr2 = new int[3][]; arr2[0] = new int[] { 1 }; arr2[1] = new int[] { 1, 2 }; arr2[2] = new int[] { 1, 2, 3 }; // [[1], [1, 2], [1, 2, 3]] System.out.println(Arrays.deepToString(arr2)); } } |
3. Initializing a 2D object array
We can also use the new operator to initialize a two-dimensional array of objects using new Type() syntax or initialize it with nulls using the index notation new Type[row][column]. For example:
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import java.util.Arrays; class Point { int x = 0, y = 0; public Point(int x, int y) { this.x = x; this.y = y; } @Override public String toString() { return "[" + x + ", " + y + "]"; } } public class Main { public static void main(String[] args) { Point[][] arr1 = { { new Point(1, 2), new Point(4, 5), new Point(0, 3) }, { new Point(8, 4), new Point(7, 8), new Point(2, 1) } }; // [[[1, 2], [4, 5], [0, 3]], [[8, 4], [7, 8], [2, 1]]] System.out.println(Arrays.deepToString(arr1)); Point[][] arr2 = new Point[2][3]; // [[null, null, null], [null, null, null]] System.out.println(Arrays.deepToString(arr2)); } } |
4. Initializing a 2D character array
To initialize a two-dimensional array of characters, we can use the String.toCharArray() method in Java. This method converts the given string into a sequence of characters and returns a newly created character array. The length of the returned array is equal to the length of the string. To illustrate, consider the following example.
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import java.util.Arrays; public class Main { public static void main(String[] args) { char[][] arr1 = { "ABCD".toCharArray(), "EF".toCharArray(), "GHI".toCharArray() }; // [[A, B, C, D], [E, F], [G, H, I]] System.out.println(Arrays.deepToString(arr1)); char[][] arr2 = { {'A', 'B', 'C', 'D'}, {'E', 'F'}, {'G', 'H', 'I'} }; // [[A, B, C, D], [E, F], [G, H, I]] System.out.println(Arrays.deepToString(arr2)); } } |
That’s all about declaring and initializing two-dimensional arrays in Java.
Thanks for reading.
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