HashMap集合类 5种最佳遍历方式

Posted 2021-03-02 luckyjcx

1. 使用 Iterator 遍历 HashMap EntrySet

 

2. 使用 Iterator 遍历 HashMap KeySet

 

3. 使用 For-each 循环迭代 HashMap

 

4. 使用 Lambda 表达式遍历 HashMap

 

5. 使用 Stream API 遍历 HashMap

 

显示例子：

 

1. 使用 Iterator 遍历 HashMap EntrySet

package com.jia.map;

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


public class HashMapDemo {

    public static void main(String[] args) {

        Map<Integer,String> map = new HashMap<>();
        map.put(1,"java");
        map.put(2,"c");
        map.put(3,"c++");
        map.put(4,"c#");
        map.put(5,"spring");
　　　　
        Iterator<Map.Entry<Integer, String>> iterator = map.entrySet().iterator();
        while (iterator.hasNext()){
            Map.Entry<Integer, String> entry = iterator.next();
            System.out.println(entry.getKey() + "：" + entry.getValue());

        }
    }
}

Output:

1：java
2：c
3：c++
4：c#
5：spring

Process finished with exit code 0

 

2. 使用 Iterator 遍历 HashMap KeySet

package com.jia.map;

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


public class HashMapDemo02 {
    
    public static void main(String[] args) {
        
        Map<Integer,String> map = new HashMap<>();
        map.put(1,"java");
        map.put(2,"c");
        map.put(3,"c++");
        map.put(4,"c#");
        map.put(5,"spring");

        Iterator<Integer> iterator = map.keySet().iterator();
        while (iterator.hasNext()){
            Integer key = iterator.next();
            System.out.println(key);
            System.out.println(map.get(key));
        }
    }
}

Output:

1
java
2
c
3
c++
4
c#
5
spring

Process finished with exit code 0

 

3. 使用 For-each 循环遍历 HashMap

package com.jia.map;

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


public class HashMapDemo03 {

    public static void main(String[] args) {

        Map<Integer,String> map = new HashMap<>();
        map.put(1,"java");
        map.put(2,"c");
        map.put(3,"c++");
        map.put(4,"c#");
        map.put(5,"spring");

        for (Map.Entry<Integer, String> entry : map.entrySet()) {
            System.out.println(entry.getKey() + "：" + entry.getValue());
        }
    }
}

Output:

1：java
2：c
3：c++
4：c#
5：spring

Process finished with exit code 0

 

4. 使用 Lambda 表达式遍历 HashMap（推荐！！！）

package com.jia.map;

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


public class HashMapDemo04 {

    public static void main(String[] args) {

        Map<Integer,String> map = new HashMap<>();
        map.put(1,"java");
        map.put(2,"c");
        map.put(3,"c++");
        map.put(4,"c#");
        map.put(5,"spring");

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

Output:

1：java
2：c
3：c++
4：c#
5：spring

Process finished with exit code 0

 

5. 使用 Stream API 遍历 HashMap（推荐！！！）

package com.jia.map;

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


public class HashMapDemo05 {

    public static void main(String[] args) {

        Map<Integer,String> map = new HashMap<>();
        map.put(1,"java");
        map.put(2,"c");
        map.put(3,"c++");
        map.put(4,"c#");
        map.put(5,"spring");

        map.entrySet().stream().forEach((entry) ->{
            System.out.println(entry.getKey() + "：" + entry.getValue());
        });
    }
}

Output:

1：java
2：c
3：c++
4：c#
5：spring

Process finished with exit code 0