遍历hashmap的6种方法

1、 通过ForEach循环进行遍历

mport java.io.IOException;
import java.util.HashMap;
import java.util.Map;

public class Test {
    public static void main(String[] args) throws IOException {
        Map<Integer, Integer> map = new HashMap<Integer, Integer>();
        map.put(1, 10);
        map.put(2, 20);

        // Iterating entries using a For Each loop
        for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
            System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());
        }

    }
}

2、 ForEach迭代键值对方式

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

public class Test {
    public static void main(String[] args) throws IOException {
        Map<Integer, Integer> map = new HashMap<Integer, Integer>();
        map.put(1, 10);
        map.put(2, 20);

        // 迭代键
        for (Integer key : map.keySet()) {
            System.out.println("Key = " + key);
        }

        // 迭代值
        for (Integer value : map.values()) {
            System.out.println("Value = " + value);
        }
    }
}

3、使用带泛型的迭代器进行遍历

import java.io.IOException;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

public class Test {
    public static void main(String[] args) throws IOException {
        Map<Integer, Integer> map = new HashMap<Integer, Integer>();
        map.put(1, 10);
        map.put(2, 20);

        Iterator<Map.Entry<Integer, Integer>> entries = map.entrySet().iterator();
        while (entries.hasNext()) {
            Map.Entry<Integer, Integer> entry = entries.next();
            System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());
        }
    }
}

4、使用不带泛型的迭代器进行遍历

import java.io.IOException;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

public class Test {

    public static void main(String[] args) throws IOException {

        Map map = new HashMap();
        map.put(1, 10);
        map.put(2, 20);

        Iterator<Map.Entry> entries = map.entrySet().iterator();
        while (entries.hasNext()) {
            Map.Entry entry = (Map.Entry) entries.next();
            Integer key = (Integer) entry.getKey();
            Integer value = (Integer) entry.getValue();
            System.out.println("Key = " + key + ", Value = " + value);
        }
    }
}

5、通过Java8 Lambda表达式遍历

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

public class Test {

    public static void main(String[] args) throws IOException {

        Map<Integer, Integer> map = new HashMap<Integer, Integer>();
        map.put(1, 10);
        map.put(2, 20);
        map.forEach((k, v) -> System.out.println("key: " + k + " value:" + v));
    }
}

6、使用 Stream API 遍历 HashMap

package com.java.tutorials.iterations;  

import java.util.HashMap;
import java.util.Map;  

/**
 * 在 Java 中遍历 HashMap 的5种最佳方法
 * @author Ramesh Fadatare
 *
 */
public class IterateHashMapExample {
    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, "Spring Framework");
        coursesMap.put(5, "Hibernate ORM framework");  

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