Java 如何打印出哈希图中的所有键？
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How do I print out all keys in hashmap?
提问by Gurkang
I'm trying to learn how hashmaps work and I've been fiddling with a small phonebook program.
我正在尝试了解哈希图的工作原理，并且一直在摆弄一个小型电话簿程序。
But I'm stumped at what to do when I want to print out all the keys.
但是当我想打印出所有的键时，我不知道该怎么做。
here's my code:
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));
}
}
采纳答案by nafas
Here we go:
开始了：
System.out.println(phoneBook.keySet());
This will printout the set of keys in your Map using Set.toString() method. for example :
这将使用 Set.toString() 方法打印出 Map 中的一组键。例如 ：
["a","b"]
回答by jjlema
Maps have a method called KeySet with all the keys.
Maps 有一个名为 KeySet 的方法，其中包含所有键。
Set<K> keySet();
回答by BullyWiiPlaza
You need to get the keySetfrom your hashMapand iterate it using e.g. a foreachloop. This way you're getting the keyswhich can then be used to get the valuesout of the map.
您需要keySet从您的中获取hashMap并使用例如循环对其进行迭代foreach。通过这种方式，您将获得keys可用于values从地图中取出的 。
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()
{
for (String variableName : phoneBook.keySet())
{
String variableKey = variableName;
String variableValue = phoneBook.get(variableName);
System.out.println("Name: " + variableKey);
System.out.println("Number: " + variableValue);
}
}
public void lookUpNumber(String name)
{
System.out.println(phoneBook.get(name));
}
public static void main(String[] args)
{
MapTester tester = new MapTester();
tester.enterNumber("A name", "A number");
tester.enterNumber("Another name", "Another number");
tester.printAll();
}
}
