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? trueIs 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? trueIs 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。