Java ConcurrentMap用法及代码示例

// Java Program to illustrate methods 
// of ConcurrentMap interface 
import java.util.concurrent.*; 
  
class ConcurrentMapDemo { 
  
    public static void main(String[] args) 
    { 
        // Since ConcurrentMap is an interface, 
        // we create instance using ConcurrentHashMap 
        ConcurrentMap<Integer, String> m = new ConcurrentHashMap<Integer, String>(); 
        m.put(100, "Geeks"); 
        m.put(101, "For"); 
        m.put(102, "Geeks"); 
  
        // Here we cant add Hello because 101 key 
        // is already present 
        m.putIfAbsent(101, "Hello"); 
  
        // We can remove entry because 101 key 
        // is associated with For value 
        m.remove(101, "For"); 
  
        // Now we can add Hello 
        m.putIfAbsent(101, "Hello"); 
  
        // We can replace Hello with For 
        m.replace(101, "Hello", "For"); 
        System.out.println("Map contents : " + m); 
    } 
}

// Java Program to demonstrate adding 
// elements 
  
import java.util.concurrent.*; 
  
class AddingElementsExample { 
    public static void main(String[] args) 
    { 
        // Instantiate an object 
        // Since ConcurrentMap 
        // is an interface so We use 
        // ConcurrentSkipListMap 
        ConcurrentMap<Integer, Integer> mpp = new ConcurrentSkipListMap<Integer, Integer>(); 
  
        // Adding elements to this map 
          // using put() method 
        for (int i = 1; i <= 5; i++) 
            mpp.put(i, i); 
  
        // Print map to the console 
        System.out.println("After put(): " + mpp); 
    } 
}

// Java Program to demonstrate removing 
// elements 
  
import java.util.concurrent.*; 
  
class RemovingElementsExample { 
    public static void main(String[] args) 
    { 
        // Instantiate an object 
        // Since ConcurrentMap 
        // is an interface so We use 
        // ConcurrentSkipListMap 
        ConcurrentMap<Integer, Integer> mpp = new ConcurrentSkipListMap<Integer, Integer>(); 
  
        // Adding elements to this map 
        // using put method 
        for (int i = 1; i <= 5; i++) 
            mpp.put(i, i); 
  
        // remove() mapping associated 
        // with key 1 
        mpp.remove(1); 
  
        System.out.println("After remove(): " + mpp); 
    } 
}

// Java Program to demonstrate accessing 
// elements 
  
import java.util.concurrent.*; 
  
class AccessingElementsExample { 
  
    public static void main(String[] args) 
    { 
  
        // Instantiate an object 
        // Since ConcurrentMap 
        // is an interface so We use 
        // ConcurrentSkipListMap 
        ConcurrentMap<Integer, String> chm = new ConcurrentSkipListMap<Integer, String>(); 
  
        // insert mappings using put method 
        chm.put(100, "Geeks"); 
        chm.put(101, "for"); 
        chm.put(102, "Geeks"); 
        chm.put(103, "Contribute"); 
  
        // Displaying the HashMap 
        System.out.println("The Mappings are: "); 
        System.out.println(chm); 
  
        // Display the value of 100 
        System.out.println("The Value associated to "
                           + "100 is : " + chm.get(100)); 
  
        // Getting the value of 103 
        System.out.println("The Value associated to "
                           + "103 is : " + chm.get(103)); 
    } 
}

import java.util.concurrent.*; 
import java.util.*; 
  
public class TraversingExample { 
  
    public static void main(String[] args) 
    { 
  
        // Instantiate an object 
        // Since ConcurrentMap 
        // is an interface so We use 
        // ConcurrentSkipListMap 
        ConcurrentMap<Integer, String> chmap = new ConcurrentSkipListMap<Integer, String>(); 
  
        // Add elements using put() 
        chmap.put(8, "Third"); 
        chmap.put(6, "Second"); 
        chmap.put(3, "First"); 
        chmap.put(11, "Fourth"); 
  
        // Create an Iterator over the 
        // ConcurrentSkipListMap 
        Iterator<ConcurrentSkipListMap 
                     .Entry<Integer, String> > itr 
            = chmap.entrySet().iterator(); 
  
        // The hasNext() method is used to check if there is 
        // a next element The next() method is used to 
        // retrieve the next element 
        while (itr.hasNext()) { 
            ConcurrentSkipListMap 
                .Entry<Integer, String> entry 
                = itr.next(); 
            System.out.println("Key = " + entry.getKey() 
                               + ", Value = "
                               + entry.getValue()); 
        } 
    } 
}