Java 8 foreach :

Java 8 introduced foreach as a method from the Iterable interface, which performs the given action for the Iterable until all elements have been processed.

This tutorials is about how to use foreach in Java 8 when we are looping the List and Map. And also how to filter the list items using Stream.filter().

Java 8 foreach for List :

In the previous versions of Java, we used to loop the list of items using foreach loop like below.

List<String> list = new ArrayList<String>();

    list.add("Java");

    list.add("Spring");

    list.add("Hibernate");

    list.add("JQuery");

    list.add("AngularJs");

    list.add("Java 8 Foreach");
    for (String cources : list) {
      System.out.println(cources);
    }

From Java8, we can loop the same thing with lambda expressions like below.

list.forEach(cource -> System.out.println(cource));

foreach with filter :

We can apply the filters for the list items, while iterating the foreach in Java 8.

list.stream().filter(cources -> cources.contains("Java 8 Foreach"))
                .forEach(System.out::println);

Example for Java 8 foreach :

Java8_Foreach.java
package com.onlinetutorialspoint.java8;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class Java8_Foreach {
  public static void normalLoop(List<String> list) {
    for (String cources : list) {
      System.out.println(cources);
    }
  }

  public static void java8Loop_Lambda(List<String> list) {
    list.forEach(cource -> System.out.println(cource));
  }

  public static void java8Loop_MethodReference(List<String> list) {
    list.forEach(System.out::println);
  }

  public static void java8Loop_Stream_Filter(List<String> list) {
    list.stream().filter(cources -> cources.contains("Java 8 Foreach")).forEach(System.out::println);
  }

  public static void main(String args[]) {
    List<String> list = new ArrayList<String>();
    list.add("Java");
    list.add("Spring");
    list.add("Hibernate");
    list.add("JQuery");
    list.add("AngularJs");
    list.add("Java 8 Foreach");
    java8Loop_Stream_Filter(list);
  }
}
Output
Java 8 Foreach

foreach with Map :

We have discussed in the previous tutorials, how to iterate the map in java in previous versions. Now this is the time to loop over the Map using Java 8 foreach method.

Legacy way to loop the Map :

for (Map.Entry<Integer, String> entry : javaVersionMap.entrySet()) {
      System.out.println("Version (" + entry.getKey() + ") : " + entry.getValue());
    }

foreach using lambda in Map:

for (Map.Entry<Integer, String> entry : javaVersionMap.entrySet()) {
      System.out.println("Version (" + entry.getKey() + ") : " + entry.getValue());
    }

foreach using lambda in Map Example :

Java8_ForeachMap.java
public class Java8_ForeachMap {
  public static void java8Loop_Lambda(Map<Integer, String> javaVersionMap) {
    javaVersionMap.forEach((k, v) -> System.out.println("Version (" + k + ") : " + v));
  }

  public static void main(String args[]) {
    Map<Integer, String> javaVersionMap = new HashMap<Integer, String>();
    javaVersionMap.put(1, "The first version was released on January 23, 1996");
    javaVersionMap.put(2, "Swing Graphical API and Collection Framework");
    javaVersionMap.put(3, "Java Namining and Directory Interfaces included");
    javaVersionMap.put(4, "assert keyword, Exception chaining and Regular Expressions ");
    javaVersionMap.put(5, "Generics, Enumarations, varargs and static imports");
    javaVersionMap.put(6, "JDBC 4 Support and JAXB 2.0 upgradation");
    javaVersionMap.put(7, "JVM Supports dynaminc languages, Stirngs in switch");
    javaVersionMap.put(8, "Lambda expressions, Functional Programming and more..");
    java8Loop_Lambda(javaVersionMap);
  }
}
Output
Version (1) : The first version was released on January 23, 1996
Version (2) : Swing Graphical API and Collection Framework
Version (3) : Java Namining and Directory Interfaces included
Version (4) : assert keyword, Exception chaining and Regular Expressions
Version (5) : Generics, Enumarations, varargs and static imports
Version (6) : JDBC 4 Support and JAXB 2.0 upgradation
Version (7) : JVM Supports dynaminc languages, Stirngs in switch
Version (8) : Lambda expressions, Functional Programming and more..

 

Happy Learning 🙂

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