Explanation on how to determine the default initialization value of Java one-dimensional array and two-dimensional array elements

1. Arrays and array elements

• Arrays in Java are reference types

• The elements of an array can be basic types or references Type, clarifying the type of array elements can help us understand the default initialization of array elements

2. One-dimensional array

The default initialization value of one-dimensional array elements is divided into There are two types, the elements are basic data types and reference data types

1. When the elements are basic data types

• ##Integer types (byte, short, int, long ) The default initial value is 0

• Floating point type (float, double) The default initial value is 0.0

• Boolean type (boolean) The default initial value is flase

• Character type (char) The default initial value is 0 (null character)

Note that the 0 here is different from the 0 of the integer type and not the character "0". This refers to the decimal 0 in the ASCII code table below

##Now we test the following code to deepen our understanding

public class Test {
	public static void main(String[] args) {
		char[] a = new char[2];
		
		if(a[0] == 0) {
			System.out.println("这是判断0的" + a[0] + "测试！");
		}
		
		if(a[0] == '0') {
			System.out.println("这是判断字符'0'的" + a[0] + "测试！");
		}
	}
}

The running results are as follows

Through the results we found The value of a[0] is judged to be 0 instead of the character '0'. When printed, a[0] is actually a null character (this is not a space!!!)

2. The array elements are reference types When

the element is a reference type, the default initial value is null

3. Two-dimensional array

A two-dimensional array in Java actually uses a one-dimensional array as an element of the array The interpretation of the default initialization value of the two-dimensional array composed of

is divided into two situations (the writing format of the following two situations is represented by int, and int can be replaced by other data types)

1 . int[][] arr = new int[2][2]

①Outer element (arr[0], arr[1]): address value
②Inner element (arr[0][0]): Use the default initial value of the one-dimensional array to determine
2. int[][] arr = new int[2][]

①Outer element (arr[0], arr[1]): address value
②Inner element (arr[0][0]): Null pointer exception
We understand it with the following figure, because the two-dimensional array is actually an array of arrays, and the outer layer saves is the address value, the inner layer can naturally judge based on the one-dimensional array

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