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    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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