Runnable Interface in Java

In this article, we will learn about the Runnable interface and its usage with examples.

The Runnable interface should be implemented by any class whose instances are intended to be executed by a thread. The Runnable interface defines a single run() method, which contains a code that executed in the thread. The Runnable object is passed to the Thread constructor.

Runnable Interface Source Code in Java Library

package
 
java.lang
;

@FunctionalInterface
public
 
interface
 
Runnable
 {
     
public
 
abstract
 
void
 
run
();
}

Runnable interface is a functional interface so we can use Runnable interface.

Note thatinterface is a functional interface so we can use Java 8 Lambda Expressions on ainterface.

Runnable Interface Method

The Runnable interface defines a single method, run, meant to contain the code executed in the thread.

• void run() – When an object implementing interface Runnable is used to create a thread, starting the thread causes the object’s run method to be called in that separately executing thread.

Runnable Interface Examples

Let’s demonstrate how to use Runnable interface with an example.

First, create a Task or WorkerThread using Runnable interface.

WorkerThread.java

public
 
class
 
WorkerThread
 
implements
 
Runnable
 {
    
private
 
String
 data;
 
    
public
 
WorkerThread
(
final
 
String
 
anyData
) {
        
this
.
data 
=
 anyData;
    }
 
    
@Override
    
public
 
void
 
run
() {
        
for
 (
int
 i 
=
 
0
; i 
<
 
5
; i
++
) {
            
System
.
out
.
println(
"
[
"
 
+
 
Thread
.
currentThread()
.
getName() 
+
 
"
] [data=
"
 
+
 
            
this
.
data 
+
 
"
] Message 
"
 
+
 i);
             
try
 {
                  
Thread
.
sleep(
200
);
             } 
catch
 (
final
 
InterruptedException
 e) {
                 e
.
printStackTrace();
             }
        }
    }
}

Second, let’s see how to use WorkerThread in the main thread. in this example the main() method is the main thread which will create another using above WorkerThread class.

public
 
class
 
InstantiateUsingRunnable
 {
 
    
public
 
static
 
void
 
main
(
final
 
String
[] 
args
) {
  
       
System
.
out
.
println(
"
Thread main started
"
);
  
       
final
 
Thread
 thread1 
=
 
new
 
Thread
(
new
 
WorkerThread
(
"
Process data through Runnable interface
"
)); 
       thread1
.
start();
       thread1
.
setName(
"
Demo Thread
"
);
  
       
System
.
out
.
println(
"
Thread main finished
"
);
   }
}

Output:

Thread main started
Thread main finished
[Demo Thread] [data=Process data through Runnable interface] Message 0
[Demo Thread] [data=Process data through Runnable interface] Message 1
[Demo Thread] [data=Process data through Runnable interface] Message 2
[Demo Thread] [data=Process data through Runnable interface] Message 3
[Demo Thread] [data=Process data through Runnable interface] Message 4

Runnable Interface Example using Anonymous Class

Anonymous classes enable you to make your code more concise. They enable you to declare and instantiate a class at the same time:

public
 
class
 
RunnableExampleUsingAnonymousClass
 {

    
public
 
static
 
void
 
main
(
final
 
String
[] 
args
) {
        
System
.
out
.
println(
"
 main thread started : 
"
 
+
 
Thread
.
currentThread()
.
getName());

        
System
.
out
.
println(
"
Creating Runnable...
"
);

        
final
 
Runnable
 runnable 
=
 
new
 
Runnable
() {
   
            
@Override
            
public
 
void
 
run
() {
                
System
.
out
.
println(
"
Inside : 
"
 
+
 
Thread
.
currentThread()
.
getName()); 
            }
        }; 

        
System
.
out
.
println(
"
Creating Thread...
"
);
        
final
 
Thread
 thread 
=
 
new
 
Thread
(runnable);

        
System
.
out
.
println(
"
Starting Thread...
"
);
        thread
.
start();
        
        
System
.
out
.
println(
"
 main thread ended : 
"
 
+
 
Thread
.
currentThread()
.
getName());
    }
}

Output:

 main thread started : main
Creating Runnable...
Creating Thread...
Starting Thread...
 main thread ended : main
Inside  : Thread-0

Runnable Interface Example Using Lambda Expression

The above example can be made even shorter by using Java 8 Lambda Expressions

public
 
class
 
RunnableExampleUsingLambda
 {

    
public
 
static
 
void
 
main
(
final
 
String
[] 
args
) {
        
System
.
out
.
println(
"
 main thread started : 
"
 
+
 
Thread
.
currentThread()
.
getName());

        
System
.
out
.
println(
"
Creating Runnable...
"
);

        
final
 
Runnable
 runnable 
=
 () 
-
>
 
System
.
out
.
println(
"
Inside  : 
"
 
+
 
Thread
.
currentThread()
.
getName()); 

        
System
.
out
.
println(
"
Creating Thread...
"
);
        
final
 
Thread
 thread 
=
 
new
 
Thread
(runnable);

        
System
.
out
.
println(
"
Starting Thread...
"
);
        thread
.
start();
        
        
System
.
out
.
println(
"
 main thread ended : 
"
 
+
 
Thread
.
currentThread()
.
getName());
    }
}

Output:

Creating Runnable...
Creating Thread...
Starting Thread...
 main thread ended : main
Inside  : Thread-0

Reference