二维为空的2D数组如何工作? [英] How do 2D arrays with the second dimension empty work?

问题描述

我无法理解以下代码:

String [][] abc = new String [4][];

这是否会创建2行的4行数组，但每一行都是空的?每行都有初始值吗?如果每一行都有特定数量的行，那么初始值是什么?

Would this create the 2d array of 4 rows but each row is empty? Is an initial value given for each row? If each row gets a specific number of rows, what would the initial value be?

推荐答案

这会创建2行的4行数组，但每一行都是空吗?

Would this create the 2d array of 4 rows but each row is empty?

它创建4行2D数组.

每一行都有初始值吗?

Is an initial value given for each row?

默认情况下，每行为 null .

如果每一行都有特定数量的行，则初始行将是什么值得吗?

If each row gets a specific number of rows, what would the initial value be?

每行可以有不同数量的元素

Each row can have a different number of elements

示例程序:

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        String[][] abc = new String[4][];
        for (String[] s : abc)
            System.out.println(s);

        // You can initialize in this way
        abc[0] = new String[] { "Sam", "John", "Chris" };

        String[] str = { "ab", "bc", "cd", "ef" };
        // You can initialize also in this way
        abc[1] = str;

        // You can initialize also in this way
        abc[2] = new String[2];
        abc[2][0] = "Hello";
        abc[2][1] = "World";

        abc[3] = new String[4];

        for (String[] s : abc)
            System.out.println(Arrays.toString(s));
    }
}

输出:

null
null
null
null
[Sam, John, Chris]
[ab, bc, cd, ef]
[Hello, World]
[null, null, null, null]

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