在Java中打印HashMap [英] Printing HashMap In Java

问题描述

我有一个HashMap：

  private HashMap< TypeKey，TypeValue> example = new HashMap< TypeKey，TypeValue>（）; 
  

现在我想运行所有的值并打印它们。

我这样写：

  for（TypeValue name：this.example.keySet（））{ 
 
 System.out.println（name）; 
} 
  

似乎不起作用。

有什么问题？

编辑：
另一个问题： /download.oracle.com/javase/6/docs/api/java/util/HashMap.html#keySet%28%29> keySet（）只返回一组key在你的hashmap，你应该迭代

在你的示例中，hashmap键的类型是 TypeKey ，但是在您的通用for循环中指定了 TypeValue ，因此无法编译。您应该将其更改为：

  for（TypeKey name：example.keySet（））{
 
 String key = name.toString（）; 
 String value = example.get（name）.toString（）; 
 System.out.println（key ++ value）; 
 
 
} 
  

如果您不需要打印

另一个问题：这个集合
是零吗？基础？我的意思是如果它有1个键
，值将是0或1？

c $ c> keySet（）是一个设置< /a>。您无法使用索引从集合中获取值，因此不是基于零或基于一的问题。如果您的hashmap有一个键，返回的keySet（）将在其中有一个条目，其大小为1.

I have a HashMap:

private HashMap<TypeKey,TypeValue > example= new HashMap<TypeKey, TypeValue>();

Now I would Like to run through all the values and print them.

I wrote this:

for (TypeValue name: this.example.keySet()){

        System.out.println(name);
} 

It doesn't seem to work.

What is the problem?

EDIT: Another question: Is this collection zero based? I mean if it has 1 key and value will the size be 0 or 1?

解决方案

keySet() only returns a set of key in your hashmap , you should iterate this key set and the get the value from the hashmap using these keys .

In your example , the type of the hashmap 's key is TypeKey , but you specified TypeValue in your generic for-loop , so it cannot be compiled. You should change it to :

for (TypeKey name: example.keySet()){

            String key =name.toString();
            String value = example.get(name).toString();  
            System.out.println(key + " " + value);  


} 

If you don't require to print key value and just need the hashmap value , you can use others' suggestion .

Another question: Is this collection is zero base? I mean if it has 1 key and value will it size be 0 or 1?

The collection returned from keySet() is a Set.You cannot get the value from a Set using an index , so it is not an question whether it is zero-based or one-based. If your hashmap has one key , the keySet() returned will has one entry inside , and its size is 1.

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