Java中Hashtable类java.util.Hashtable.containsKey()方法用于检查Hashtable中是否存在特定键。它将key元素作为参数,如果表中存在该元素,则返回True。

句法:

Hash_table.containsKey(key_element)

参数:该方法只接受一个参数key_element,该参数指的是应该在Hashtable中检查其存在的密钥。

返回值:如果密钥存在于Hashtable中,则该方法返回boolean true,否则返回false。

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

程序1:

// Java code to illustrate the containsKey() method
import java.util.*;
 
public class Hash_Table_Demo {
    public static void main(String[] args)
    {
 
        // Creating an empty Hashtable
        Hashtable<Integer, String> hash_table = 
        new Hashtable<Integer, String>();
 
        // Putting values into the table
        hash_table.put(10, "Geeks");
        hash_table.put(15, "4");
        hash_table.put(20, "Geeks");
        hash_table.put(25, "Welcomes");
        hash_table.put(30, "You");
 
        // Displaying the Hashtable
        System.out.println("Initial Table is: " + hash_table); 
 
        // Checking for the key_element '20'
        System.out.println("Is the key '20' present? " + 
        hash_table.containsKey(20));
 
        // Checking for the key_element '5'
        System.out.println("Is the key '5' present? " + 
        hash_table.containsKey(5));
    }
}

输出:

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

程序2:

// Java code to illustrate the containsKey() method
import java.util.*;
 
public class Hash_Table_Demo {
    public static void main(String[] args)
    {
 
        // Creating an empty Hashtable
        Hashtable<String, Integer> hash_table= 
        new Hashtable<String, Integer>();
 
        // Putting values into the table
        hash_table.put("Geeks", 10);
        hash_table.put("4", 15);
        hash_table.put("Geeks", 20);
        hash_table.put("Welcomes", 25);
        hash_table.put("You", 30);
 
        // Displaying the Hashtable
        System.out.println("Initial Table is: " + hash_table);
 
        // Checking for the key_element 'Welcomes'
        System.out.println("Is the key 'Welcomes' present? " + 
        hash_table.containsKey("Welcomes"));
 
        // Checking for the key_element 'World'
        System.out.println("Is the key 'World' present? " + 
        hash_table.containsKey("World"));
    }
}

输出:

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

注意:可以使用任何类型的变体和不同数据类型的组合执行相同的操作。

 
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