Java Collections synchronizedMap()方法及实例

java.util.Collections 类的 synchronizedMap() 方法是用来返回一个由指定Map支持的同步（线程安全）Map。为了保证串行访问，对支持Map的所有访问都要通过返回的Map完成，这一点非常关键。

语法

public static <K, V> Map<K, V> synchronizedMap(Map<K, V> m)

参数： 该方法将Map作为参数，被 “包裹 “在一个同步Map中。

返回值： 该方法返回一个指定Map的同步视图。

下面是说明synchronizedMap()方法的例子。

例1 :

// Java program to demonstrate
// synchronizedMap() method
// for <String, String> Value
  
import java.util.*;
  
public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {
  
        try {
  
            // creating object of Map<String, String>
            Map<String, String>
                map = new HashMap<String, String>();
  
            // populate the map
            map.put("Value1", "20");
            map.put("Value2", "30");
            map.put("Value3", "40");
  
            // printing the Collection
            System.out.println("Map : " + map);
  
            // create a synchronized map
            Map<String, String>
                synmap = Collections.synchronizedMap(map);
  
            // printing the Collection
            System.out.println("Synchronized map is : "
                               + synmap);
        }
  
        catch (IllegalArgumentException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出。

Map : {Value3=40, Value1=20, Value2=30}
Synchronized map is : {Value3=40, Value1=20, Value2=30}

例2:

// Java program to demonstrate
// synchronizedMap() method
// for <String, Boolean> Value
  
import java.util.*;
  
public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {
  
        try {
  
            // creating object of Map<String, Boolean>
            Map<String, Boolean>
                map = new HashMap<String, Boolean>();
  
            // populate the map
            map.put("Bramha", true);
            map.put("Vishnu", true);
            map.put("Mahesh", true);
  
            // printing the Collection
            System.out.println("Map : " + map);
  
            // create a synchronized map
            Map<String, Boolean>
                synmap = Collections.synchronizedMap(map);
  
            // printing the Collection
            System.out.println("Synchronized map is : "
                               + synmap);
        }
        catch (IllegalArgumentException e) {
  
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出。

Map : {Bramha=true, Vishnu=true, Mahesh=true}
Synchronized map is : {Bramha=true, Vishnu=true, Mahesh=true}