遍歷 HashMap 的 5 種最佳方式:

package com.tang;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import org.junit.Test;

/**
 * 遍歷 HashMap 的 5 種最佳方式:
 * 
 * 1.使用 Iterator 遍歷 HashMap EntrySet
 * 
 * 2.使用 Iterator 遍歷HashMap KeySet
 * 
 * 3.使用 For-each 循環迭代 HashMap
 * 
 * 4.使用 Lambda 表達式遍歷 HashMap
 * 
 * 5.使用 Stream API 遍歷 HashMap
 * 
 *
 */
public class TestMap {
//	1.使用 Iterator 遍歷 HashMap EntrySet
	@Test
	public void test1() {
		Map<Integer, String> hashMap = new HashMap<Integer, String>();
		hashMap.put(1, "JAVA");
		hashMap.put(2, "Python");
		hashMap.put(3, "C");
		hashMap.put(4, "C++");
		hashMap.put(5, "C#");
		hashMap.put(6, "Scala");

		Iterator<Entry<Integer, String>> iterator = hashMap.entrySet().iterator();
		while (iterator.hasNext()) {
			Entry<Integer, String> next = iterator.next();
			System.out.println(next.getKey() + " " + next.getValue());
		}
	}

//	2.使用 Iterator 遍歷HashMap KeySet
	@Test
	public void test2() {
		Map<Integer, String> hashMap = new HashMap<Integer, String>();
		hashMap.put(1, "JAVA");
		hashMap.put(2, "Python");
		hashMap.put(3, "C");
		hashMap.put(4, "C++");
		hashMap.put(5, "C#");
		hashMap.put(6, "Scala");

		Iterator<Integer> iterator = hashMap.keySet().iterator();
		while (iterator.hasNext()) {
			Integer key = iterator.next();
			String string = hashMap.get(key);
			System.out.println(key + " " + string);
		}
	}

//	3.使用 For-each 循環迭代 HashMap
	@Test
	public void test3() {
		Map<Integer, String> hashMap = new HashMap<Integer, String>();
		hashMap.put(1, "JAVA");
		hashMap.put(2, "Python");
		hashMap.put(3, "C");
		hashMap.put(4, "C++");
		hashMap.put(5, "C#");
		hashMap.put(6, "Scala");

		for (Map.Entry<Integer, String> entrySet : hashMap.entrySet()) {
			Integer key = entrySet.getKey();
			String value = entrySet.getValue();
			System.out.println(key + " " + value);
		}
	}

	@Test
//	4.使用 Lambda 表達式遍歷 HashMap
	public void test4() {
		Map<Integer, String> hashMap = new HashMap<Integer, String>();
		hashMap.put(1, "JAVA");
		hashMap.put(2, "Python");
		hashMap.put(3, "C");
		hashMap.put(4, "C++");
		hashMap.put(5, "C#");
		hashMap.put(6, "Scala");

		hashMap.forEach((key, value) -> {
			System.out.println(key + " " + value);
		});
	}

	@Test
//	5.使用 Stream API 遍歷 HashMap
	public void test5() {
		Map<Integer, String> hashMap = new HashMap<Integer, String>();
		hashMap.put(1, "JAVA");
		hashMap.put(2, "Python");
		hashMap.put(3, "C");
		hashMap.put(4, "C++");
		hashMap.put(5, "C#");
		hashMap.put(6, "Scala");
		hashMap.entrySet().stream().forEach((entry) -> {
			System.out.println(entry.getKey() + " " + entry.getValue());
		});
	}

}