Java ConcurrentHashMap contains()方法及示例

Java.util.ConcurrentHashMap的contains()方法用于检查某些键是否映射到该表的指定值中。它是一种执行特定任务的传统方法。该操作类似于ConcurrentHashMap的containsValue()方法。

语法

ConcurrentHashMap.contains(Object Value)

参数： 该方法只需要一个对象类型的参数Value，指的是其映射应该被地图内的任何键检查的值。

返回值： 如果检测到该值的映射，该方法返回布尔值true，否则返回false。

下面的程序用来说明ConcurrentHashMap.containsValue()方法的工作。

程序1： 将字符串值映射到整数键。

// Java code to illustrate the contains() method
  
import java.util.*;
import java.util.concurrent.*;
  
public class ConcurrentHashMapDemo {
    public static void main(String[] args)
    {
  
        // Creating an empty HashMap
        ConcurrentHashMap<Integer, String>
            hash_map = new ConcurrentHashMap<Integer,
                                             String>();
  
        // Mapping string values to int keys
        hash_map.put(10, "Geeks");
        hash_map.put(15, "4");
        hash_map.put(20, "Geeks");
        hash_map.put(25, "Welcomes");
        hash_map.put(30, "You");
  
        // Displaying the ConcurrentHashMap
        System.out.println("Initial Mappings are: "
                           + hash_map);
  
        // Checking for the Value 'Geeks'
        System.out.println("Is the value 'Geeks' present? "
                           + hash_map.containsValue("Geeks"));
  
        // Checking for the Value 'World'
        System.out.println("Is the value 'World' present? "
                           + hash_map.containsValue("World"));
    }
}

输出:

Initial Mappings are: {20=Geeks, 25=Welcomes, 10=Geeks, 30=You, 15=4}
Is the value 'Geeks' present? true
Is the value 'World' present? false

程序2： 将整数值映射到字符串键。

// Java code to illustrate the contains() method
  
import java.util.*;
import java.util.concurrent.*;
  
public class ConcurrentHashMapDemo {
    public static void main(String[] args)
    {
  
        // Creating an empty ConcurrentHashMap
        ConcurrentHashMap<String, Integer>
            hash_map = new ConcurrentHashMap<String,
                                             Integer>();
  
        // Mapping int values to string keys
        hash_map.put("Geeks", 10);
        hash_map.put("4", 15);
        hash_map.put("Geeks", 20);
        hash_map.put("Welcomes", 25);
        hash_map.put("You", 30);
  
        // Displaying the ConcurrentHashMap
        System.out.println("Initial Mappings are: "
                           + hash_map);
  
        // Checking for the Value 'Geeks'
        System.out.println("Is the value 'Geeks' present? "
                           + hash_map.contains(25));
  
        // Checking for the Value 'World'
        System.out.println("Is the value 'World' present? "
                           + hash_map.contains(35));
    }
}

输出:

Initial Mappings are: {4=15, Geeks=20, You=30, Welcomes=25}
Is the value 'Geeks' present? true
Is the value 'World' present? false

注意： 同样的操作可以通过不同数据类型的变化和组合对任何类型的Mapping进行操作。