Java 5种HashMap 的遍历方式

package mian;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
public class Demo {
    public static void main(String[] args) {

        Map<Integer,String> coursesMap = new HashMap<Integer, String>();

        coursesMap.put(1,"c");
        coursesMap.put(2,"c++");
        coursesMap.put(3,"java");
        coursesMap.put(4,"python");

        // 1. 使用 Iterator 遍历 HashMap EntrySet
        Iterator<Entry< Integer, String >> iterator = coursesMap.entrySet().iterator();
        while (iterator.hasNext()) {
            Entry< Integer, String > entry = iterator.next();
            System.out.println(entry.getKey());
            System.out.println(entry.getValue());
        }

        // 2. 使用 Iterator 遍历 HashMap KeySet
        Iterator <Integer> iterator1 = coursesMap.keySet().iterator();
        while (iterator1.hasNext()) {
            Integer key = iterator1.next();
            System.out.println(key);
            System.out.println(coursesMap.get(key));
        }

        // 3. 使用 For-each 循环遍历 HashMap
        for (Map.Entry < Integer, String > entry: coursesMap.entrySet()) {
            System.out.println(entry.getKey());
            System.out.println(entry.getValue());
        }

        // 4. 使用 Lambda 表达式遍历 HashMap
        coursesMap.forEach((key, value) -> {
            System.out.println(key);
            System.out.println(value);
        });

        // 5. 使用 Stream API 遍历 HashMap
        coursesMap.entrySet().stream().forEach((entry) -> {
            System.out.println(entry.getKey());
            System.out.println(entry.getValue());
        });

    }
}