Java的：重复检测ArrayList中？ [英] Java: Detect duplicates in ArrayList?

问题描述

我怎么能去检测（返回真/假）一个ArrayList是否包含Java中的相同元素的多个？

How could I go about detecting (returning true/false) whether an ArrayList contains more than one of the same element in Java?

非常感谢，
特里

Many thanks, Terry

修改
忘了提，我不是在寻找比较块与对方但他们的整数值。每个块有一个int，这是什么使他们不同。
我通过调用一个名为getNum的方法找到特定地块的INT（例如表1 [0] [2] .getNum（）;

Edit Forgot to mention that I am not looking to compare "Blocks" with each other but their integer values. Each "block" has an int and this is what makes them different. I find the int of a particular Block by calling a method named "getNum" (e.g. table1[0][2].getNum();

推荐答案

最简单的：转储整个集合到一个组（使用（集合）集合构造或Set.addAll），然后看是否设置有大小相同该ArrayList

Simplest: dump the whole collection into a Set (using the Set(Collection) constructor or Set.addAll), then see if the Set has the same size as the ArrayList.

List<Integer> list = ...;
Set<Integer> set = new HashSet<Integer>(list);

if(set.size() < list.size()){
    /* There are duplicates */
}

更新：如果我正确理解你的问题，你有块的二维数组，如

Update: If I'm understanding your question correctly, you have a 2d array of Block, as in

块表[] [];

和要检测，如果其中任何行有重复？

and you want to detect if any row of them has duplicates?

在这种情况下，我可以做到以下几点，假设座实现等于和散列code正确的：

In that case, I could do the following, assuming that Block implements "equals" and "hashCode" correctly:

for (Block[] row : table) {
   Set set = new HashSet<Block>(); 
   for (Block cell : row) {
      set.add(cell);
   }
   if (set.size() < 6) { //has duplicate
   }
}

我不是100％肯定的，对于语法，所以它可能是更安全的把它写成

I'm not 100% sure of that for syntax, so it might be safer to write it as

for (int i = 0; i < 6; i++) {
   Set set = new HashSet<Block>(); 
   for (int j = 0; j < 6; j++)
    set.add(table[i][j]);

...

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