java - 检查数组中是否存在空元素

Question

我想检查数组元素是否为空。

我已经初始化了一个大小为 2 的 String 数组。我循环遍历该数组并检查数组元素是否为 null。如果它为空，我将仅在该位置添加一个String“a”。

下面的代码将产生以下输出:

1=a
2=a

代码:

public class CheckArrayElementIsNull {
    public static void main(String[] args) {
        String[] arr = new String[2];       
        for(int i = 0; i < arr.length; i++) {
            if(arr[i] == null) {
                arr[i] = "a";
            }
            System.out.println(i + "=" + arr[i]);   
            if(arr[i] == null) {
                System.out.println(i + "= null");
            }
        }
    }
}

我尝试在 if 条件后添加一个中断，但没有打印出任何内容。

 public class CheckArrayElementIsNull {
    public static void main(String[] args) {
        String[] arr = new String[2];       
        for(int i = 0; i < arr.length; i++) {
            if(arr[i] == null) {
                arr[i] = "a"; 
                break;
            }
            System.out.println(i + "=" + arr[i]);   
            if(arr[i] == null) {
                System.out.println(i + "= null");
            }
        }
    }
}

我期望这个输出:

1=a
2=null

Answer 1

您的循环中存在一些问题。

    for(int i = 1; i < arr.length - 1; i++) { //<---- This does not iterate over the entire array, leaving out the first and last elements
        if(arr[i] == null) {
            arr[i] = "a"; 
            break; //<---- This terminates the loop entirely, if you want to stop all instructions past this one try using continue instead
        }
        System.out.println(i + "=" + arr[i]);   
        if(arr[i] == null) { //This code is unreachable as arr[i] is initialized if it was detected as null before
            System.out.println(i + "= null");
        }else{
            System.out.println(i + "=" + arr[i]); 
        }
    }

相反，你应该尝试

 for(int i = 0; i < arr.length; i++) {
    if(arr[i] == null) {
        arr[i] = "a";
        System.out.println(i + "= null");
        break;
    }
    System.out.println(i + "=" + arr[i]); 
}