In order to close the Java program, we need to consider which kind of Java application it is?, because termination of Java application varies between normal core java programs to swing GUI applications. In general, all Java program terminates automatically once all user threads created by program finishes its execution, including main thread. JVM doesn't wait for the daemon thread so as soon as the last user thread is finished, the Java program will terminate. If you want to close or terminate your java application before this your only option is to use System.exit(int status) or Runtime.getRuntime().exit().
This causes JVM to abandon all threads and exit immediately. Shutdown hooks are get called to allow some last-minute clearing before JVM actually terminates. System.exit() also accept an int status parameter where a non-zero value denotes abnormal execution and its result returned by java command to the caller.
In this java tutorial, we will see an example of closing both the Java program and the Java Swing application. This is also a good swing interview question that you can ask any GUI developer and my second article in the swing after writing invokeAndWait vs invokeLater
This causes JVM to abandon all threads and exit immediately. Shutdown hooks are get called to allow some last-minute clearing before JVM actually terminates. System.exit() also accept an int status parameter where a non-zero value denotes abnormal execution and its result returned by java command to the caller.
In this java tutorial, we will see an example of closing both the Java program and the Java Swing application. This is also a good swing interview question that you can ask any GUI developer and my second article in the swing after writing invokeAndWait vs invokeLater
1. Example of Closing Java program using System.exit()
Here is a code example of closing the Java program by calling System.exit() method. Remember non zero arguments to exit() method like exit(1) denotes abnormal termination of Java application.
import java.util.logging.Level;
import java.util.logging.Logger;
/**
*Java program which terminates itself by using System.exit() method , non zero call to exit() method denotes abnormal termination.
*/
public class JavaCloseExample {
public static void main(String args[]) throws InterruptedException {
Thread t = new Thread(){
@Override
public void run(){
while(true){
System.out.println("User thread is running");
try {
Thread.sleep(100);
} catch (InterruptedException ex) {
Logger.getLogger(JavaCloseExample.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
};
t.start();
Thread.sleep(200);
System.out.println("terminating or closing java program");
System.exit(1); //non zero value to exit says abnormal termination of JVM
}
}
Output:
User thread is running
User thread is running
terminating or closing java program
Java Result: 1 //1 is what we passed to exit() method
import java.util.logging.Logger;
/**
*Java program which terminates itself by using System.exit() method , non zero call to exit() method denotes abnormal termination.
*/
public class JavaCloseExample {
public static void main(String args[]) throws InterruptedException {
Thread t = new Thread(){
@Override
public void run(){
while(true){
System.out.println("User thread is running");
try {
Thread.sleep(100);
} catch (InterruptedException ex) {
Logger.getLogger(JavaCloseExample.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
};
t.start();
Thread.sleep(200);
System.out.println("terminating or closing java program");
System.exit(1); //non zero value to exit says abnormal termination of JVM
}
}
Output:
User thread is running
User thread is running
terminating or closing java program
Java Result: 1 //1 is what we passed to exit() method
This Java program first creates a Thread in the main method and start it which prints “User thread is running” and then main thread sleep for 200 Millisecond, till then other user thread is running and printing but once main thread woken up it terminates the program by calling exit() method of java.lang.System class.
2. How to close Java swing application from the program
Swing application mostly uses JFrame as a top-level container which provides two options to close swing GUI application from code. The first option which is the default is EXIT_ON_CLOSE which terminates the Java swing GUI program when you click the close button on the JFrame window. Another option is DISPOSE_ON_CLOSE which terminates JVM if the last displayable window is disposed of. Difference between EXIT_ON_CLOSE and DISPOSE_ON_CLOSE is that if you have a non-daemon thread running it will not be closed in case of DISPOSE_ON_CLOSE, while EXIT_ON_CLOSE terminate JVM even if user thread is running.
Run the below example by uncommenting DISPOSE_ON_CLOSE in your IDE and you can see user thread running even after clicking on the close button. here is a complete code example of closing the Swing application in Java.
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JFrame;
/**
* Java swing program which terminates itself by calling EXIT_ON_CLOSE and DISPOSE_ON_CLOSE
*/
public class CloseSwingExample {
public static void main(String args[]) throws InterruptedException {
JFrame frame = new JFrame("Sample");
//frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE); won't terminate JVM if user thread running
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(200, 200);
frame.setVisible(true);
Thread t = new Thread() {
@Override
public void run() {
while (true) {
System.out.println("User thread is running");
try {
Thread.sleep(100);
} catch (InterruptedException ex) {
Logger.getLogger(CloseSwingExample.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
};
t.start();
}
}
import java.util.logging.Logger;
import javax.swing.JFrame;
/**
* Java swing program which terminates itself by calling EXIT_ON_CLOSE and DISPOSE_ON_CLOSE
*/
public class CloseSwingExample {
public static void main(String args[]) throws InterruptedException {
JFrame frame = new JFrame("Sample");
//frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE); won't terminate JVM if user thread running
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(200, 200);
frame.setVisible(true);
Thread t = new Thread() {
@Override
public void run() {
while (true) {
System.out.println("User thread is running");
try {
Thread.sleep(100);
} catch (InterruptedException ex) {
Logger.getLogger(CloseSwingExample.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
};
t.start();
}
}
3. Important points about terminating or closing Java program
Few points worth noting regarding close or termination of Java application from the program itself:
1) System.exit() actually calls Runtime.getRuntime().exit() method.
2) Non-zero arguments to exit() denotes abnormal termination of Java program.
3) Shutdown hooks are executed before the Java program actually terminates.
4) There are two options to close the Java Swing application one is EXIT_ON_CLOSE and the other is DISPOSE_ON_CLOSE.
5) DISPOSE_ON_CLOSE doesn't terminate JVM if any user thread is running.
6) You can also implement a window listener to implement your closing mechanism by using System.exit() in the Swing application.
That's all on how to close or terminate the Java program. we have also seen an example of closing the Swing application in Java and the difference between EXIT_ON_CLOSE and DISPOSE_ON_CLOSE.
Other Java programming tutorials you may find useful:
Best way to terminate Java program is not to abort it and let it complete by itself :). if you want to quit than there is only one option System.exit(), Runtime.exit() is just copy of it.
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