05_04_hashmap遍历的方法

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));
    }
}

1、 通过ForEach循环进行遍历

1.  
   mport java.io.IOException;
2.  
   import java.util.HashMap;
3.  
   import java.util.Map;
4.  
    
5.  
   public class Test {
6.  
   public static void main(String[] args) throws IOException {
7.  
   Map<Integer, Integer> map = new HashMap<Integer, Integer>();
8.  
   map.put(1, 10);
9.  
   map.put(2, 20);
10.  
     
11.  
    // Iterating entries using a For Each loop
12.  
    for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
13.  
    System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());
14.  
    }
15.  
     
16.  
    }
17.  
    }

2、 ForEach迭代键值对方式

如果你只想使用键或者值，推荐使用如下方式

1.  
   import java.io.IOException;
2.  
   import java.util.HashMap;
3.  
   import java.util.Map;
4.  
    
5.  
   public class Test {
6.  
   public static void main(String[] args) throws IOException {
7.  
   Map<Integer, Integer> map = new HashMap<Integer, Integer>();
8.  
   map.put(1, 10);
9.  
   map.put(2, 20);
10.  
     
11.  
    // 迭代键
12.  
    for (Integer key : map.keySet()) {
13.  
    System.out.println("Key = " + key);
14.  
    }
15.  
     
16.  
    // 迭代值
17.  
    for (Integer value : map.values()) {
18.  
    System.out.println("Value = " + value);
19.  
    }
20.  
    }
21.  
    }

3、使用带泛型的迭代器进行遍历

1.  
   import java.io.IOException;
2.  
   import java.util.HashMap;
3.  
   import java.util.Iterator;
4.  
   import java.util.Map;
5.  
    
6.  
   public class Test {
7.  
   public static void main(String[] args) throws IOException {
8.  
   Map<Integer, Integer> map = new HashMap<Integer, Integer>();
9.  
   map.put(1, 10);
10.  
    map.put(2, 20);
11.  
     
12.  
    Iterator<Map.Entry<Integer, Integer>> entries = map.entrySet().iterator();
13.  
    while (entries.hasNext()) {
14.  
    Map.Entry<Integer, Integer> entry = entries.next();
15.  
    System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());
16.  
    }
17.  
    }
18.  
    }

4、使用不带泛型的迭代器进行遍历

1.  
   import java.io.IOException;
2.  
   import java.util.HashMap;
3.  
   import java.util.Iterator;
4.  
   import java.util.Map;
5.  
    
6.  
   public class Test {
7.  
    
8.  
   public static void main(String[] args) throws IOException {
9.  
    
10.  
    Map map = new HashMap();
11.  
    map.put(1, 10);
12.  
    map.put(2, 20);
13.  
     
14.  
    Iterator<Map.Entry> entries = map.entrySet().iterator();
15.  
    while (entries.hasNext()) {
16.  
    Map.Entry entry = (Map.Entry) entries.next();
17.  
    Integer key = (Integer) entry.getKey();
18.  
    Integer value = (Integer) entry.getValue();
19.  
    System.out.println("Key = " + key + ", Value = " + value);
20.  
    }
21.  
    }
22.  
    }

5、通过Java8 Lambda表达式遍历

1.  
   import java.io.IOException;
2.  
   import java.util.HashMap;
3.  
   import java.util.Map;
4.  
    
5.  
   public class Test {
6.  
    
7.  
   public static void main(String[] args) throws IOException {
8.  
    
9.  
   Map<Integer, Integer> map = new HashMap<Integer, Integer>();
10.  
    map.put(1, 10);
11.  
    map.put(2, 20);
12.  
    map.forEach((k, v) -> System.out.println("key: " + k + " value:" + v));
13.  
    }
14.  
    }