在Java中遍历对象的TreeMap（不是字符串！）

Question

I've got a Treemap of Servers:

TreeMap server_map = new TreeMap<String, Server>() ;

I'd like to iterate over the whole map to print all the servers. Using this kind of loop:

for (Map.Entry<String, Server> entry : server_map.entrySet())
{
    System.out.println(entry.getKey() + "/" + entry.getValue().foo);
}

This won't work, because there is an Unresolved compilation problem:

Type mismatch: cannot convert from element type Object to Map.Entry

Isn't there a possibility to iterate over a Treemap of servers?

Answer 1

将声明更改为此：

TreeMap<String, Server> server_map = new TreeMap<String, Server>() ;

Answer 2

还要注意，由于java7不需要在右侧声明泛型类型，因此可以使用菱形运算符，从而节省了一些编写工作。

TreeMap<String, Server> server_map = new TreeMap<>() ;

Answer 3

In Java 8 you can do it this way:

TreeMap server_map = new TreeMap();
for (Map.Entry entry : server_map.entrySet()){
 System.out.println(entry.getKey() + "/" + ((Server)entry.getValue()).foo);
}

I just solved a problem similar to this one by doing something like this. If you use the <String, Server> way it will want you to use java 1.5 syntax.