如何在hashmap中打印出所有键？

Question

我正在尝试学习哈希图如何工作,而我一直在摆弄一个小型的电话簿程序.

但是当我想要打印出所有按键时,我很难过.

这是我的代码:

import java.util.HashMap;
import java.util.*;

public class MapTester
{

private HashMap<String, String> phoneBook;

public MapTester(){
   phoneBook = new HashMap<String, String>();
}

public void enterNumber(String name, String number){
   phoneBook.put(name, number);
}

public void printAll(){
    //This is where I want to print all. I've been trying with iterator and foreach, but I can't get em to work
}

   public void lookUpNumber(String name){
    System.out.println(phoneBook.get(name));
}
}

Answer 1

开始了:

System.out.println(phoneBook.keySet());

这将使用Set.toString()方法在Map中打印出一组键.例如 :

["a","b"]