JAVA ArrayList:如何知道它是否包含String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);
            }
        }
    }

控制台说假". 我有一个ArrayList，我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方法实现检查对象的相等性.但是，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，传递给contains方法的new String[]{"one", "abc"})将创建一个 new 数组，该数组将与最初添加到ArrayList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.

一种检查方法是遍历ArrayList中的每个数组，并使用Arrays.equals(array1, array2)检查是否相等:

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commons-lang的nofollow> ArrayUtils.isEquals .

Another way is to use ArrayUtils.isEquals from Apache commons-lang.

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