JAVA ArrayList:如何知道它是否包含字符串数组? [英] JAVA ArrayList : How to know whether it contains a String array or not?

问题描述

import java.util.ArrayList;    
public class Test {
        public static void main (String[] args){
            ArrayList<String[]> a = new ArrayList<String[]>();
            a.add(new String[]{"one", "abc"});
            a.add(new String[]{"two", "def"});
            if(a.contains(new String[]{"one", "abc"})){
                System.out.println(true);
            }else{
                System.out.println(false);
            }
        }
    }

控制台说错误".我有一个 ArrayList，但无法检查它是否包含特定的 String 数组.怎么做，为什么?

Console said "false." I have an ArrayList and I can't check whether it contains a particular String array. How to do and why?

推荐答案

contains 使用 equals 方法实现检查对象相等性.然而，对于数组，equals 等效于引用相等.IE.array1.equals(array2) 转换为 array1 == array2.

contains checks object equality using the equals method implementation. For arrays, however, equals is equivalent to reference equality. I.e. array1.equals(array2) translates to array1 == array2.

在上面，new String[]{"one", "abc"}) 传递给contains 方法会创建一个newem> 数组，它将与最初添加到 ArrayList 中的数组不同.

In the above, the new String[]{"one", "abc"}) passed to the contains method will create a new array which will be different than the one originally added to the ArrayList.

进行检查的一种方法是遍历 ArrayList 中的每个数组，并使用 Arrays.equals(array1, array2) 来检查相等性:

One way to do the check is to loop over each array in the ArrayList and check the equality using Arrays.equals(array1, array2):

for(String[] arr : a) {
        if(Arrays.equals(arr, new String[]{"one", "abc"})) {
            System.out.println(true);
            break;
        }
}

另一种方法是使用 ArrayUtils.isEquals 来自 Apache commons-lang.

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