Java 中的 Hashtable containsKey()方法
原文:https://www . geesforgeks . org/hashtable-contains key-method-in-Java/
Java . util . Hashtable . Contains KeY()方法用于检查哈希表中是否存在特定的键。它将键元素作为参数，如果表中存在该元素，则返回 True。
语法:
Hash_table.containsKey(*key_element*)
参数:该方法只取一个参数 key_element ，它指的是应该在哈希表中检查其存在的键。
返回值:如果键存在于哈希表中，该方法返回布尔真，否则返回假。
下面的程序用来说明 Java . util . hashtable . contains key()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));
}
}
Output:
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"));
}
}
Output:
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:相同的操作可以用任何类型的变异和不同数据类型的组合来执行。
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