Java HashMap 删除键/值

发布于 2024-11-17 17:44:29 字数 500 浏览 2 评论 0原文

我只是在寻找关于为什么最好迭代 HashMap 的解释和/或见解。

例如，下面的代码（在我看来）的作用完全相同（或者应该如此）。但是，如果我不迭代 HashMap，则不会删除键。

_adjacentNodes.remove(node);        

Iterator<Map.Entry<String, LinkedList<Node>>> iterator = _adjacentNodes.entrySet().iterator();
while (iterator.hasNext()) {
     Map.Entry<String, LinkedList<Node>> entry = iterator.next();
     if(node.getNodeID().contentEquals(entry.getKey())){
          iterator.remove();
     }
}

到底是怎么回事？

原文

I'm just looking for an explanation and/or insight as to why its better to iterate over a HashMap.

For instance the code below (in my eyes) does the exact same (or it should). However if I don't iterate over the HashMap the key is not removed.

_adjacentNodes.remove(node);        

Iterator<Map.Entry<String, LinkedList<Node>>> iterator = _adjacentNodes.entrySet().iterator();
while (iterator.hasNext()) {
     Map.Entry<String, LinkedList<Node>> entry = iterator.next();
     if(node.getNodeID().contentEquals(entry.getKey())){
          iterator.remove();
     }
}

What is going on?

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凉城已无爱 2024-11-24 17:44:29

由于您的键是字符串，因此您应该删除字符串而不是节点。所以尝试一下

_adjacentNodes.remove(node.getNodeID());

Since your key is a String you should remove String not Node. So try

_adjacentNodes.remove(node.getNodeID());

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活雷疯 2024-11-24 17:44:29

remove() 确实按预期工作。例如，给定这个程序：

import java.util.HashMap;


public class HashMapExample {
    public static void main(String[] args) {
        HashMap<String, Integer> map = new HashMap<String, Integer>();

        map.put("a", 1);
        map.put("b", 2);

        System.out.println("Before removal");
        for( String s : map.keySet() ) {
            System.out.println( s );
        }

        System.out.println("\n\nAfter removal");

        map.remove("a");
        for( String s : map.keySet() ) {
            System.out.println( s );
        }
    }
}

这将输出以下内容：

Before removal
b
a


After removal
b

我能想到的唯一出错的事情是您试图在开始时删除的节点对象与您从迭代器获得的节点对象不是同一节点对象。也就是说，它们具有相同的“NodeID”，但是不同的对象。也许您值得检查一下remove()的返回值。

编辑：哈，我没有发现字符串/对象错误，但至少我们走在正确的道路上；）

remove() does work as expected. For example given this program:

import java.util.HashMap;


public class HashMapExample {
    public static void main(String[] args) {
        HashMap<String, Integer> map = new HashMap<String, Integer>();

        map.put("a", 1);
        map.put("b", 2);

        System.out.println("Before removal");
        for( String s : map.keySet() ) {
            System.out.println( s );
        }

        System.out.println("\n\nAfter removal");

        map.remove("a");
        for( String s : map.keySet() ) {
            System.out.println( s );
        }
    }
}

This will output the following:

Before removal
b
a


After removal
b

The only thing I can think of which is going wrong is that the node object you are trying to remove at the start is not the same node object as the one you get from the iterator. That is, they have the same 'NodeID' but are different objects. Perhaps it is worth it for you to check the return of remove().

Edit: Ha I didn't spot the String/Object mistake but at least we were going down the right path ; )

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