How do I check whether a thread group has been destroyed?

By Wayan in Core API, Lang Package 0 Comment

You can use ThreadGroup.isDestroyed() method to check whether a thread group and its subgroups has been destroyed.

package org.kodejava.lang;

public class CheckGroupDestroy {
    public static void main(String[] args) {
        ThreadGroup grandParent = new ThreadGroup("GrandParent");
        ThreadGroup uncle = new ThreadGroup(grandParent, "Uncle");
        ThreadGroup parent = new ThreadGroup(grandParent, "Parent");
        ThreadGroup son = new ThreadGroup(parent, "Son");
        ThreadGroup daughter = new ThreadGroup(parent, "Daughter");
        ThreadGroup neighbour = new ThreadGroup("Neighbour");

        ThreadGroup[] groupArray = {
                grandParent, uncle, parent, son, daughter, neighbour
        };

        // Destroy 'parent' group and all its subgroups
        parent.destroy();

        // Check whether the group is destroyed. The result is,
        // GrandParent, Uncle, and Neighbour did not destroyed
        // because they are not Parent's subgroups
        for (ThreadGroup tg : groupArray) {
            if (tg.isDestroyed()) {
                System.out.println(tg.getName() + " is destroyed");
            } else {
                System.out.println(tg.getName() + " is not destroyed");
            }
        }
    }
}

The result is:

GrandParent is not destroyed
Uncle is not destroyed
Parent is destroyed
Son is destroyed
Daughter is destroyed
Neighbour is not destroyed

How do I destroy a thread group?

By Wayan in Core API, Lang Package 0 Comment

You can destroy a thread group by using destroy() method of ThreadGroup class. It will cleans up the thread group and removes it from the thread group hierarchy. It’s not only destroy the thread group, but also all its subgroups.

The destroy() method is of limited use: it can only be called if there are no threads presently in the thread group.

package org.kodejava.lang;

public class ThreadGroupDestroy {
    public static void main(String[] args) {
        ThreadGroup root = new ThreadGroup("Root");
        ThreadGroup server = new ThreadGroup(root, "ServerGroup");
        ThreadGroup client = new ThreadGroup(root, "ClientGroup");

        // Destroy 'root' thread groups and all its subgroup
        // ('server' & 'client')
        root.destroy();

        // Check if 'root' group and its subgroups already destroyed
        if (root.isDestroyed()) {
            System.out.println("Root group is destroyed");
        }

        if (server.isDestroyed()) {
            System.out.println("Server group is destroyed");
        }

        if (client.isDestroyed()) {
            System.out.println("Client group is destroyed");
        }
    }
}

How do I use multi-catch statement?

By Wayan in Core API, Lang Package 1 Comment

The multi-catch is a language enhancement feature introduces in the Java 7. This allows us to use a single catch block to handle multiple exceptions. Each exception is separated by the pipe symbol (|).

Using the multi-catch simplify our exception handling and also reduce code duplicates in the catch block. Let’s see an example below:

package org.kodejava.lang;

import java.io.IOException;
import java.sql.SQLException;

public class MultiCatchDemo {
    public static void main(String[] args) {
        MultiCatchDemo demo = new MultiCatchDemo();
        try {
            demo.callA();
            demo.callB();
            demo.callC();
        } catch (IOException | SQLException | ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    private void callA() throws IOException {
        throw new IOException("IOException");
    }

    private void callB() throws SQLException {
        throw new SQLException("SQLException");
    }

    private void callC() throws ClassNotFoundException {
        throw new ClassNotFoundException("ClassNotFoundException");
    }
}

How do I get thread group of a thread?

By Wayan in Core API, Lang Package 0 Comment

Use the getThreadGroup() method of Thread class to get the thread group to which the thread belongs.

package org.kodejava.lang;

public class GetThreadGroup {
    public static void main(String[] args) {
        // Create thread groups
        ThreadGroup group = new ThreadGroup("ThreadGroup");
        ThreadGroup anotherGroup = new ThreadGroup(group, "AnotherGroup");

        // Create threads and placed into thread group
        Thread t1 = new Thread(group, new FirstThread(), "Thread1");
        Thread t2 = new Thread(anotherGroup, new FirstThread(), "Thread2");

        // Start the threads
        t1.start();
        t2.start();

        // Use getThreadGroup() method of Thread class to get the object
        // of ThreadGroup then use the getName() method to get the name
        // of thread group.
        System.out.format("%s is a member of %s%n", t1.getName(),
                t1.getThreadGroup().getName());
        System.out.format("%s is a member of %s%n", t2.getName(),
                t2.getThreadGroup().getName());
    }
}

class FirstThread implements Runnable {
    public void run() {
        System.out.println("Start..");
    }
}

How do I get the state of a thread?

By Wayan in Core API, Lang Package 0 Comment

To get the state of a thread use getState() method of a Thread class. One thing to be noted is that this method is designed for use in monitoring of the system state, not for synchronization control.

package org.kodejava.lang;

public class GetThreadState implements Runnable {
    public static void main(String[] args) {
        Thread thread = new Thread(new GetThreadState());
        thread.start();

        // Get the state of the thread.
        Thread.State state = thread.getState();
        System.out.println("State: " + state.name());
    }

    public void run() {
        System.out.println("Start..");
    }
}