HashTable forEach() method in Java with Examples

The forEach(BiConsumer) method of Hashtable class perform the BiConsumer operation on each entry of hashtable until all entries have been processed or the action throws an exception. The BiConsumer operation is a function operation of key-value pair of hashtable performed in the order of iteration. Method traverses each element of Hashtable until all elements have been processed by the method or an exception occurs. Exceptions thrown by the Operation are passed to the caller.

Syntax:

public void 
    forEach(BiConsumer<? super K, ? super V> action)

Parameters: This method takes a parameter name BiConsumer which represents the action to be performed for each element.

Returns: This method returns nothing.

Exception: This method throws:

  • NullPointerException: if the specified action is null.

Below programs illustrate the forEach(BiConsumer) method:

Program 1:

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// Java program to demonstrate
// forEach(BiConsumer) method.
  
import java.util.*;
  
public class GFG {
  
    // Main method
    public static void main(String[] args)
    {
  
        // crete a table and add some values
        Map<String, Integer>
            table = new Hashtable<>();
  
        table.put("Pen", 10);
        table.put("Book", 500);
        table.put("Clothes", 400);
        table.put("Mobile", 5000);
        table.put("Booklet", 2500);
  
        // add 100 in each value using forEach()
        table.forEach((k, v) -> {
  
            v = v + 100;
            table.replace(k, v);
        });
  
        // print new mapping using forEcah()
        table.forEach(
            (k, v) -> System.out.println("Key : " + k + ", Value : " + v));
    }
}

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Output:

Key : Booklet, Value : 2600
Key : Clothes, Value : 500
Key : Mobile, Value : 5100
Key : Pen, Value : 110
Key : Book, Value : 600

Program 2: To Show NullPointerException

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// Java program to demonstrate
// forEach(BiConsumer) method.
  
import java.util.*;
  
public class GFG {
  
    // Main method
    public static void main(String[] args)
    {
  
        // crete a table and add some values
        Map<Integer, String>
            table = new Hashtable<>();
  
        table.put(1, "100RS");
        table.put(2, "500RS");
        table.put(3, "1000RS");
  
        try {
  
            // add 100 in each value using forEach()
            table.forEach((k, v) -> {
  
                v = v + 100;
                table.put(null, v);
            });
        }
        catch (Exception e) {
  
            System.out.println("Exception: " + e);
        }
    }
}

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Output:

Exception: java.lang.NullPointerException

References: https://docs.oracle.com/javase/8/docs/api/java/util/Hashtable.html#forEach-java.util.function.BiConsumer-



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