Java中的 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此表中的指定值。这是执行特定任务的传统方法。操作类似于 ConcurrentHashMap 的 containsValue() 方法。

句法：

ConcurrentHashMap.contains(Object Value)

参数：该方法只接受一个 Object 类型的参数Value ，它指的是映射应该由映射中的任何键检查的值。

返回值：如果检测到值的映射，则该方法返回布尔值 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
            hash_map = new ConcurrentHashMap();
  
        // 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
            hash_map = new ConcurrentHashMap();
  
        // 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：可以对任何类型的映射执行相同的操作，这些映射具有不同数据类型的变化和组合。