Callable Java Example Java 8

Java 8 Runnable and Callable Lambda Example with Argument

May 22, 2016

On this page we will provide Java 8 Runnable and Callable lambda example with argument. In java 8 Runnable and Callable both interface have been annotated by @FunctionalInterface. We can implement run() and call() method using lambda expression. Here on this page we will also provide how to pass arguments to Runnable and Callable methods.

Java 8 Runnable Lambda Example with Argument

Java 8 supports lambda expression. In java 8 Runnable interface has been annotated with @FunctionalInterface. Now we can create Runnable instance using lambda expression.

Runnable r = () -> System.out.println("Hello World!"); Thread th = new Thread(r); th.start();            

The above code is equivalent to below code.

Runnable r = new Runnable() {    @Override    public void run() { 	System.out.println("Hello World!");    } }; Thread th = new Thread(r); th.start();            

In case we need to write more than one line of code inside run() method, we can do using lambda expression as given below.

Runnable r = () -> { 	Consumer<Book> style = (Book b) -> System.out.println("Book Id:"+b.getId() + ", Book Name:"+b.getName()); 	list.forEach(style); };            

To pass the argument to our run() method we should use final modifier.

final List<Book> list =  Arrays.asList(new Book(1, "Ramayan"), new Book(2, "Mahabharat")); Runnable r = () -> { 	Consumer<Book> style = (Book b) -> System.out.println("Book Id:"+b.getId() + ", Book Name:"+b.getName()); 	list.forEach(style); };            

Now find the complete example of Java 8 Runnable with lambda expression using Thread class.
Java8RunnableDemo.java

package com.concretepage.runnable; import java.util.Arrays; import java.util.List; import java.util.function.Consumer; import com.concretepage.Book; public class Java8RunnableDemo { 	public static void main(String[] args) { 		final List<Book> list =  Arrays.asList(new Book(1, "Ramayan"), new Book(2, "Mahabharat")); 		Runnable r1 = () -> list.forEach(Book::print); 		Thread th1 = new Thread(r1); 		th1.start(); 		Runnable r2 = () -> { 			Consumer<Book> style = (Book b) -> System.out.println("Book Id:"+b.getId() + ", Book Name:"+b.getName()); 			list.forEach(style); 		}; 		Thread th2 = new Thread(r2); 		th2.start(); 	} }            

Book.java

package com.concretepage; public class Book {         public int id;         public String name;         public Book(int id, String name){             this.id = id;             this.name = name;         }         public int getId() { 		return id; 	} 	public void setId(int id) { 		this.id = id; 	} 	public String getName() { 		return name; 	} 	public void setName(String name) { 		this.name = name; 	} 	public void print(){                System.out.println("id:"+id + ", Name:"+name);         } }            

Find the output.

id:1, Name:Ramayan Book Id:1, Book Name:Ramayan id:2, Name:Mahabharat Book Id:2, Book Name:Mahabharat

Find the sample code to run the Runnable instance using ExecutorService.
Java8RunnableDemoExecutor.java

package com.concretepage.runnable; import java.util.Arrays; import java.util.List; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.function.Consumer; import com.concretepage.Book; public class Java8RunnableDemoExecutor { 	public static void main(String[] args) { 		final List<Book> list =  Arrays.asList(new Book(1, "Ramayan"), new Book(2, "Mahabharat")); 		ExecutorService service =  Executors.newFixedThreadPool(2); 		Runnable r1 = () -> list.forEach(Book::print); 		service.execute(r1); 		Runnable r2 = () -> { 			Consumer<Book> style = (Book b) -> System.out.println("Book Id:"+b.getId() + ", Book Name:"+b.getName()); 			list.forEach(style); 		}; 		service.execute(r2); 	} }            

Find the output.

id:1, Name:Ramayan id:2, Name:Mahabharat Book Id:1, Book Name:Ramayan Book Id:2, Book Name:Mahabharat

Java 8 Callable Lambda Example with Argument

Callable<V> interface has been introduced in Java 5 where V is a return type. In Java 8, Callable interface has been annotated with @FunctionalInterface. Now in java 8, we can create the object of Callable using lambda expression as follows.

Callable<Integer> callableObj = () -> { return 2*3; };            

The above code is equivalent to below code snippet.

Callable<Integer> callableObj = new Callable<Integer>() { 	@Override 	public Integer call() throws Exception { 		return 2*3; 	} };

To pass the argument to our call() method we should use final modifier.

final int val = 10;  Callable<Integer> callableObj = () -> { return 2*val; };

Now find the complete example of Callable with lambda expression using ExecutorService.
Java8CallableDemo.java

package com.concretepage.callable; import java.util.Arrays; import java.util.List; import java.util.concurrent.Callable; import java.util.concurrent.ExecutionException; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Future; public class Java8CallableDemo { 	public static void main(String[] args) { 		final List<Integer> integers =  Arrays.asList(1,2,3,4,5); 		Callable<Integer> callableObj = () -> { 			int result = integers.stream().mapToInt(i -> i.intValue()).sum(); 			return result; 		}; 		ExecutorService service =  Executors.newSingleThreadExecutor(); 		Future<Integer> future = service.submit(callableObj); 		Integer result=0; 		try { 			result = future.get(); 		} catch (InterruptedException e) { 			e.printStackTrace(); 		} catch (ExecutionException e) { 			e.printStackTrace(); 		} 		System.out.println("Sum = "+result); 	} }

Find the output.

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Source: https://www.concretepage.com/java/jdk-8/java-8-runnable-and-callable-lambda-example-with-argument

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