Java中的WeakHashMap containsValue()方法

Java.util.WeakHashMap.containsValue() 方法用于检查 WeakHashMap 中的一个或多个键是否正在映射特定值。如果该值由映射中的任何键映射，则它将 Value 作为参数并返回 True。

句法：

Weak_Hash_Map.containsValue(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。

下面的程序说明了Java.util.WeakHashMap.containsValue() 方法：

程序 1：将字符串值映射到整数键。

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

输出：

Initial Mappings are: {30=You, 15=4, 10=Geeks, 25=Welcomes, 20=Geeks}
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 containsValue() method
import java.util.*;
  
public class Weak_Hash_Map_Demo {
    public static void main(String[] args)
    {
  
        // Creating an empty WeakHashMap
        Map weak_hash = new WeakHashMap();
  
        // Mapping int values to string keys
        weak_hash.put("Geeks", 10);
        weak_hash.put("4", 15);
        weak_hash.put("Geeks", 20);
        weak_hash.put("Welcomes", 25);
        weak_hash.put("You", 30);
  
        // Displaying the WeakHashMap
        System.out.println("Initial Mappings are: " + weak_hash);
  
        // Checking for the Value '10'
        System.out.println("Is the value '10' present? " +
                                    weak_hash.containsValue(10));
  
        // Checking for the Value '30'
        System.out.println("Is the value '30' present? " + 
                                    weak_hash.containsValue(30));
  
        // Checking for the Value '40'
        System.out.println("Is the value '40' present? " +
                                    weak_hash.containsValue(40));
    }
}

输出：

Initial Mappings are: {Welcomes=25, 4=15, You=30, Geeks=20}
Is the value '10' present? false
Is the value '30' present? true
Is the value '40' 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。