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

java.util.HashMap.containsKey()句法:

Hash_Map.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.HashMap.containsKey()的工作方法: HashMap.containsKey()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 Hash_Map_Demo {
    public static void main(String[] args)
    {

        // Creating an empty HashMap
        HashMap<Integer, String> hash_map = new HashMap<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 HashMap
        System.out.println("Initial Mappings are: " + hash_map);

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

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

输出:

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

HashMap.containsKey()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 Hash_Map_Demo {
    public static void main(String[] args)
    {

        // Creating an empty HashMap
        HashMap<String, Integer> hash_map = new HashMap<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 HashMap
        System.out.println("Initial Mappings are: " + hash_map);

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

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

输出:

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

注意:对于具有不同数据类型的变体和组合的任何类型的映射,都可以执行相同的操作。

 
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