Java中, IdentityHashMap containsKey()的方法

作者: Arvin Chen 分类: Java 发布时间: 2018-08-07 21:26

java.util.IdentityHashMap.containsKey()方法用于检查特定键是否被映射到IdentityHashMap。它将key元素作为参数,如果该元素在map中映射,则返回True。

句法:

Identity_HashMap.containsKey(key_element)

参数:该方法只接受一个参数key_element,该参数引用应在map内检查其映射的键。

返回值:如果检测到密钥的存在,则该方法返回布尔值true,否则返回false。

下面的程序用于说明java.util.IdentityHashMap.containsKey()的工作方法

程序1:将字符串值映射到整数键。

// Java code to illustrate the containsKey() method
import java.util.*;

public class Identity_Hash_Map_Demo {
    public static void main(String[] args)
    {

        // Creating an empty IdentityHashMap
        IdentityHashMap<Integer, String> identity_hash = 
                   new IdentityHashMap<Integer, String>();

        // Mapping string values to int keys
        identity_hash.put(10, "Geeks");
        identity_hash.put(15, "4");
        identity_hash.put(20, "Geeks");
        identity_hash.put(25, "Welcomes");
        identity_hash.put(30, "You");

        // Displaying the IdentityHashMap
        System.out.println("Initial Mappings are: " + 
                                          identity_hash);

        // Checking for the key_element '20'
        System.out.println("Is the key '20' present? " + 
                           identity_hash.containsKey(20));

        // Checking for the key_element '5'
        System.out.println("Is the key '5' present? " + 
                            identity_hash.containsKey(5));
    }
}

输出:

Initial Mappings are: {10=Geeks, 30=You, 20=Geeks, 25=Welcomes, 15=4}
Is the key '20' present? true
Is the key '5' present? false

程序2:将整数值映射到字符串键。

// Java code to illustrate the containsKey() method
import java.util.*;

public class Identity_Hash_Map_Demo {
    public static void main(String[] args)
    {

        // Creating an empty IdentityHashMap
        IdentityHashMap<String, Integer> identity_hash = 
                     new IdentityHashMap<String, Integer>();

        // Mapping int values to string keys
        identity_hash.put("Geeks", 10);
        identity_hash.put("4", 15);
        identity_hash.put("Geeks", 20);
        identity_hash.put("Welcomes", 25);
        identity_hash.put("You", 30);

        // Displaying the IdentityHashMap
        System.out.println("Initial Mappings are: " + 
                                              identity_hash);

        // Checking for the key_element 'Welcomes'
        System.out.println("Is the key 'Welcomes' present? " + 
                        identity_hash.containsKey("Welcomes"));

        // Checking for the key_element 'World'
        System.out.println("Is the key 'World' present? " + 
                           identity_hash.containsKey("World"));
    }
}

输出:

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