HashMap forEach(BiConsumer) method in Java with Examples

The forEach(BiConsumer) method of HashMap class perform the BiConsumer operation on each entry of hashmap until all entries have been processed or the action throws an exception. The BiConsumer operation is a function operation of the 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 action)

Parameters: This method accepts a parameter action of BiConsumer type that represents what action are to be performed on the HashMap elements.



Returns: This method do not return anything.

Exceptions: This method throws NullPointerException if the action is null.

Below programs illustrate the forEach(BiConsumer) method:

Program 1: to traverse a hashmap using action

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// Java program to demonstrate
// forEach(BiConsumer) method.
  
import java.util.HashMap;
import java.util.Map;
import java.util.function.BiConsumer;
  
public class GFG {
  
    // Main method
    public static void main(String[] args)
    {
  
        // create a HashMap and add some values
        Map<String, Integer> map
            = new HashMap<>();
  
        map.put("geeks", 55);
        map.put("for", 13);
        map.put("geeks", 22);
        map.put("is", 11);
        map.put("heaven", 90);
        map.put("for", 100);
        map.put("geekies like us", 96);
  
        // creating a custom action
        BiConsumer<String, Integer> action
            = new MyBiConsumer();
  
        // calling forEach method
        map.forEach(action);
    }
}
  
// Defining Our Action in MyBiConsumer class
class MyBiConsumer implements BiConsumer<String, Integer> {
  
    public void accept(String k, Integer v)
    {
        System.out.print("Key = " + k);
        System.out.print("\t Value = " + v);
        System.out.println();
    }
}

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Output:

Key = geeks     Value = 22
Key = for     Value = 100
Key = is     Value = 11
Key = heaven     Value = 90
Key = geekies like us     Value = 96

Program 2:

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// Java program to demonstrate
// forEach(BiConsumer) method.
  
import java.util.HashMap;
import java.util.Map;
import java.util.function.BiConsumer;
  
public class GFG {
  
    // Main method
    public static void main(String[] args)
    {
  
        // Create a HashMap
        // and add some values
        Map<String, Integer> map
            = new HashMap<>();
  
        map.put("geeks", 55);
        map.put("for", 13);
        map.put("geeks", 22);
        map.put("is", 11);
        map.put("heaven", 90);
        map.put("for", 100);
        map.put("geekies like us", 96);
  
        // creating an action
        BiConsumer<String, Integer> action
            = new MyBiConsumer();
  
        // calling forEach method
        map.forEach(action);
    }
}
  
// Defining Our Action in MyBiConsumer class
class MyBiConsumer implements BiConsumer<String, Integer> {
  
    public void accept(String k, Integer v)
    {
        System.out.println("Key: " + k
                           + "\tValue: " + v);
  
        if ("for".equals(k)) {
            System.out.println("Its the "
                               + "highest value\n");
        }
    }
}

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Output:

Key: geeks    Value: 22
Key: for    Value: 100
Its the highest value

Key: is    Value: 11
Key: heaven    Value: 90
Key: geekies like us    Value: 96

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



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