Java – How to close a Java Swing application from the code

javaswing

What is the proper way to terminate a Swing application from the code, and what are the pitfalls?

I'd tried to close my application automatically after a timer fires. But just calling dispose() on the JFrame didn't do the trick – the window vanished but the application did not terminate. However when closing the window with the close button, the application does terminate. What should I do?

Best Answer

Your JFrame default close action can be set to "DISPOSE_ON_CLOSE" instead of EXIT_ON_CLOSE (why people keep using EXIT_ON_CLOSE is beyond me).

If you have any undisposed windows or non-daemon threads, your application will not terminate. This should be considered a error (and solving it with System.exit is a very bad idea).

The most common culprits are java.util.Timer and a custom Thread you've created. Both should be set to daemon or must be explicitly killed.

If you want to check for all active frames, you can use Frame.getFrames(). If all Windows/Frames are disposed of, then use a debugger to check for any non-daemon threads that are still running.

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Java – What are the differences between a HashMap and a Hashtable in Java

There are several differences between HashMap and Hashtable in Java:

Hashtable is synchronized, whereas HashMap is not. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones.
Hashtable does not allow null keys or values. HashMap allows one null key and any number of null values.
One of HashMap's subclasses is LinkedHashMap, so in the event that you'd want predictable iteration order (which is insertion order by default), you could easily swap out the HashMap for a LinkedHashMap. This wouldn't be as easy if you were using Hashtable.

Since synchronization is not an issue for you, I'd recommend HashMap. If synchronization becomes an issue, you may also look at ConcurrentHashMap.

Java – How to efficiently iterate over each entry in a Java Map

Map<String, String> map = ...
for (Map.Entry<String, String> entry : map.entrySet()) {
    System.out.println(entry.getKey() + "/" + entry.getValue());
}

On Java 10+:

for (var entry : map.entrySet()) {
    System.out.println(entry.getKey() + "/" + entry.getValue());
}

Best Answer

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Java – What are the differences between a HashMap and a Hashtable in Java

Java – How to efficiently iterate over each entry in a Java Map

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