Java containsAll在给定列表时不返回true [英] Java containsAll does not return true when given lists

问题描述

我想检查一个数组是另一个数组的子集。

I want to check an array is subset of another array.

该程序打印错误，但我希望是真的。为什么不是containsAll返回true？

The program prints false, but I expect true. Why isn't containsAll returning true?

int[] subset;
subset = new int[3];
subset[0]=10;
subset[1]=20;
subset[2]=30;

int[] superset;
superset = new int[5];
superset[0]=10;
superset[1]=20;
superset[2]=30;
superset[3]=40;
superset[4]=60;
HashSet sublist = new HashSet(Arrays.asList(subset));
HashSet suplist = new HashSet(Arrays.asList(superset));
boolean isSubset = sublist.containsAll(Arrays.asList(suplist));
System.out.println(isSubset);

推荐答案

有一个微妙的错误：

new HashSet(Arrays.asList(subset));

上面的行不创建一组整数，因为你可能有预期。相反，它使用单个元素子集数组创建 HashSet< int []> 。

The above line does not create a set of integers as you might have expected. Instead, it creates a HashSet<int[]> with a single element, the subset array.

这与泛型不支持基本类型的事实有关。

This has to do with the fact that generics don't support primitive types.

你的编译器会告诉你的如果您将子列表和 suplist 声明为 HashSet< Integer> 。

Your compiler would have told you about the mistake if you declared sublist and suplist as HashSet<Integer>.

除此之外，你还有 suplist 和子列表 containsAll（）调用中的错误方法。

On top of that, you got suplist and sublist the wrong way round in the containsAll() call.

以下按预期方式工作：

    Integer[] subset = new Integer[]{10, 20, 30};
    Integer[] superset = new Integer[]{10, 20, 30, 40, 60};
    HashSet<Integer> sublist = new HashSet<Integer>(Arrays.asList(subset));
    HashSet<Integer> suplist = new HashSet<Integer>(Arrays.asList(superset));
    boolean isSubset = suplist.containsAll(sublist);
    System.out.println(isSubset);

一个关键变化是使用 Integer [] 代替 int [] 。

One key change is that this is using Integer[] in place of int[].

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