How do I get direct superclass and interfaces of a class?

By Wayan in Reflection 0 Comment

Java reflection also dealing with inheritance concepts. You can get the direct interfaces and direct super class of a class by using method getInterfaces() and getSuperclass() of java.lang.Class object.

  • getInterfaces() will returns an array of Class objects that represent the direct super interfaces of the target Class object.
  • getSuperclass() will returns the Class object representing the direct super class of the target Class object or null if the target represents Object class, an interface, a primitive type, or void.
package org.kodejava.lang.reflect;

import javax.swing.*;
import java.util.Date;

public class GetSuperClassDemo {
    public static void main(String[] args) {
        GetSuperClassDemo.get(String.class);
        GetSuperClassDemo.get(Date.class);
        GetSuperClassDemo.get(JButton.class);
        GetSuperClassDemo.get(Timer.class);
    }

    public static void get(Class<?> clazz) {
        // Gets array of direct interface of clazz object
        Class<?>[] interfaces = clazz.getInterfaces();

        System.out.format("Direct Interfaces of %s:%n",
                clazz.getName());
        for (Class<?> clz : interfaces) {
            System.out.println(clz.getName());
        }

        // Gets direct superclass of clazz object
        Class<?> superclz = clazz.getSuperclass();
        System.out.format("Direct Superclass of %s: is %s %n",
                clazz.getName(), superclz.getName());
        System.out.println("====================================");
    }
}

Here is the result of the code snippet:

Direct Interfaces of java.lang.String:
java.io.Serializable
java.lang.Comparable
java.lang.CharSequence
Direct Superclass of java.lang.String: is java.lang.Object 
====================================
Direct Interfaces of java.util.Date:
java.io.Serializable
java.lang.Cloneable
java.lang.Comparable
Direct Superclass of java.util.Date: is java.lang.Object 
====================================
Direct Interfaces of javax.swing.JButton:
javax.accessibility.Accessible
Direct Superclass of javax.swing.JButton: is javax.swing.AbstractButton 
====================================
Direct Interfaces of javax.swing.Timer:
java.io.Serializable
Direct Superclass of javax.swing.Timer: is java.lang.Object 
====================================

How do I check if a class represent an interface type?

By Wayan in Reflection 0 Comment

You can use the isInterface() method call of the java.lang.Class to identify if a class objects represent an interface type.

package org.kodejava.lang.reflect;

import java.io.Serializable;

public class IsInterfaceDemo {
    public static void main(String[] args) {
        IsInterfaceDemo.get(Serializable.class);
        IsInterfaceDemo.get(Long.class);
    }

    private static void get(Class<?> clazz) {
        if (clazz.isInterface()) {
            System.out.println(clazz.getName() +
                    " is an interface type.");
        } else {
            System.out.println(clazz.getName() +
                    " is not an interface type.");
        }
    }
}

Here is the result of the program:

java.io.Serializable is an interface type.
java.lang.Long is not an interface type.

How do I check if a class represent a primitive type?

By Wayan in Reflection 0 Comment

Java uses class objects to represent all eight primitive types. A class object that represents a primitive type can be identified using the isPrimitive() method call. void is not a type in Java, but the isPrimitive() method returns true for void.class.

package org.kodejava.lang.reflect;

public class IsPrimitiveDemo {
    public static void main(String[] args) {
        IsPrimitiveDemo.get(int.class);
        IsPrimitiveDemo.get(String.class);
        IsPrimitiveDemo.get(double.class);
        IsPrimitiveDemo.get(void.class);
    }

    private static void get(Class<?> clazz) {
        if (clazz.isPrimitive()) {
            System.out.println(clazz.getName() +
                    " is a primitive type.");
        } else {
            System.out.println(clazz.getName() +
                    " is not a primitive type.");
        }
    }
}

Here is the result of the program:

int is a primitive type.
java.lang.String is not a primitive type.
double is a primitive type.
void is a primitive type.

How do I get information regarding class name?

By Wayan in Reflection 0 Comment 
package org.kodejava.lang.reflect;

import java.util.Date;

public class ClassNameDemo {
    public static void main(String[] args) {
        Date date = new Date();

        // Gets the Class of the date instance.
        Class<?> clazz = date.getClass();

        // Gets the name of the class.
        String name = clazz.getName();
        System.out.println("Class name     : " + name);

        // Gets the canonical name of the class.
        String canonical = clazz.getCanonicalName();
        System.out.println("Canonical name : " + canonical);

        // Gets the simple name of the class.
        String simple = clazz.getSimpleName();
        System.out.println("Simple name    : " + simple);
    }
}

Here are the information printed out by the program:

Class name     : java.util.Date
Canonical name : java.util.Date
Simple name    : Date

How do I insert a text in a specified position in JTextArea?

By Wayan in Swing 0 Comment

The insert(String str, int pos) of the JTextArea allows us to insert a text at the specified position. In the example below we insert brown and over words into the current JTextArea text.

package org.kodejava.swing;

import javax.swing.*;
import java.awt.*;

public class TextAreaInsertText extends JPanel {
    public TextAreaInsertText() {
        initializeUI();
    }

    public static void showFrame() {
        JPanel panel = new TextAreaInsertText();
        panel.setOpaque(true);

        JFrame frame = new JFrame("JTextArea Demo");
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setContentPane(panel);
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(TextAreaInsertText::showFrame);
    }

    private void initializeUI() {
        String text = "The quick fox jumps the lazy dog.";

        JTextArea textArea = new JTextArea(text);
        textArea.setLineWrap(true);
        textArea.setWrapStyleWord(true);
        JScrollPane scrollPane = new JScrollPane(textArea);

        textArea.insert("brown ", 10);
        textArea.insert("over ", 26);

        this.setPreferredSize(new Dimension(500, 200));
        this.setLayout(new BorderLayout());
        this.add(scrollPane, BorderLayout.CENTER);
    }
}

The screenshot of the result from the code snippet above is:

JTextArea Insert Text Demo

How do I replace text in the JTextArea?

By Wayan in Swing 0 Comment

In this example you’ll see how to use the replaceRange(String str, int start, int end) method to replace a string in the JTextArea from the start position to the end position with the specified string.

package org.kodejava.swing;

import javax.swing.*;
import java.awt.*;

public class TextAreaReplaceText extends JPanel {
    public TextAreaReplaceText() {
        initializeUI();
    }

    public static void showFrame() {
        JPanel panel = new TextAreaReplaceText();
        panel.setOpaque(true);

        JFrame frame = new JFrame("JTextArea Demo");
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setContentPane(panel);
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(TextAreaReplaceText::showFrame);
    }

    private void initializeUI() {
        String text = "The quick white fox jumps over the sleepy dog.";

        JTextArea textArea = new JTextArea(text);
        textArea.setLineWrap(true);
        textArea.setWrapStyleWord(true);
        JScrollPane scrollPane = new JScrollPane(textArea);

        textArea.replaceRange("brown", 10, 15);
        textArea.replaceRange("lazy", 35, 41);

        this.setPreferredSize(new Dimension(500, 200));
        this.setLayout(new BorderLayout());
        this.add(scrollPane, BorderLayout.CENTER);
    }
}

The screenshot of the code snippet above is:

JTextArea Replace Text Demo

How do I select all text in JTextArea?

By Wayan in Swing 0 Comment

Selecting all text in the JTextArea component can be done by using the selectAll() method. In the example below we use a button action to do the selection. After select the text we transfer focus back to the JTextArea so that the highlighted text is shown.

package org.kodejava.swing;

import javax.swing.*;
import java.awt.*;

public class TextAreaSelectAll extends JPanel {
    public TextAreaSelectAll() {
        initializeUI();
    }

    public static void showFrame() {
        JPanel panel = new TextAreaSelectAll();
        panel.setOpaque(true);

        JFrame frame = new JFrame("JTextArea Demo");
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setContentPane(panel);
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(TextAreaSelectAll::showFrame);
    }

    private void initializeUI() {
        this.setLayout(new BorderLayout());
        this.setPreferredSize(new Dimension(500, 200));

        final JTextArea textArea = new JTextArea(
                "The quick brown fox jumps over the lazy dog.");
        textArea.setLineWrap(true);
        textArea.setWrapStyleWord(true);

        JScrollPane pane = new JScrollPane(textArea);
        pane.setPreferredSize(new Dimension(500, 200));
        pane.setVerticalScrollBarPolicy(
                JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);

        final JButton button1 = new JButton("Select All");
        button1.addActionListener(e -> {
            textArea.selectAll();

            // Transfer focus to JTextArea to show the selected
            // text.
            button1.transferFocusBackward();
        });
        final JButton button2 = new JButton("Get Selected Text");
        button2.addActionListener(e -> {
            String text = textArea.getSelectedText();
            System.out.println("Text = " + text);
        });

        JPanel buttonPanel = new JPanel(new FlowLayout());
        buttonPanel.add(button1);
        buttonPanel.add(button2);

        this.add(pane, BorderLayout.CENTER);
        this.add(buttonPanel, BorderLayout.SOUTH);
    }
}

And here the screenshot of the code snippet above:

JTextArea Select All Text

How do I append text to JTextArea?

By Wayan in Swing 2 Comments

To append text to the end of the JTextArea document we can use the append(String str) method. This method does nothing if the document is null or the string is null or empty.

package org.kodejava.swing;

import javax.swing.*;
import java.awt.*;

public class TextAreaAppendText extends JPanel {
    public TextAreaAppendText() {
        initializeUI();
    }

    public static void showFrame() {
        JPanel panel = new TextAreaAppendText();
        panel.setOpaque(true);

        JFrame frame = new JFrame("JTextArea Demo");
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setContentPane(panel);
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(TextAreaAppendText::showFrame);
    }

    private void initializeUI() {
        String text = "The quick brown fox ";

        JTextArea textArea = new JTextArea(text);
        textArea.setLineWrap(true);
        textArea.setWrapStyleWord(true);
        JScrollPane scrollPane = new JScrollPane(textArea);

        String appendText = "jumps over the lazy dog.";
        textArea.append(appendText);

        this.setPreferredSize(new Dimension(500, 200));
        this.setLayout(new BorderLayout());
        this.add(scrollPane, BorderLayout.CENTER);
    }
}

The output of the code snippet above is:

JTextArea Append Text Demo

How do I use join method to wait for threads to finish?

By Wayan in Core API, Lang Package 0 Comment

If you want a thread to work until another thread dies, you can join the thread onto the end of the another thread using the join() method. For example, you want thread B only work until thread A completes its work, then you want thread B to join thread A.

package org.kodejava.example.lang;

public class ThreadJoin implements Runnable {
    private int numberOfLoop;

    private ThreadJoin(int numberOfLoop) {
        this.numberOfLoop = numberOfLoop;
    }

    public void run() {
        System.out.println("[" +
            Thread.currentThread().getName() + "] - Running.");

        for (int i = 0; i < this.numberOfLoop; i++) {
            System.out.println("[" +
                Thread.currentThread().getName() + "] " + i);
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        System.out.println("[" +
            Thread.currentThread().getName() + "] - Done.");
    }

    public static void main(String[] args) {
        Thread t1 = new Thread(new ThreadJoin(10), "FirstThread");
        Thread t2 = new Thread(new ThreadJoin(20), "SecondThread");

        try {
            // start t1 and waits for this thread to die before
            // starting the t2 thread.
            t1.start();
            t1.join();

            // start t2
            t2.start();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

How do I set the priority of a thread?

By Wayan in Core API, Lang Package 0 Comment

Threads always run with some priority, usually represented as a number between 1 and 10 (although in some cases the range is less than 10). A thread gets a default priority that is the priority of the thread of execution that creates it.

But, you can also set a thread’s priority directly by calling the setPriority() method on a Thread instance. One thing to remember about thread priorities is never rely on thread priorities, because thread-scheduling priority behavior is not guaranteed.

package org.kodejava.lang;

public class ThreadPriority extends Thread {
    private final String threadName;

    ThreadPriority(String threadName) {
        this.threadName = threadName;
    }

    public static void main(String[] args) {
        ThreadPriority thread1 = new ThreadPriority("First");
        ThreadPriority thread2 = new ThreadPriority("Second");
        ThreadPriority thread3 = new ThreadPriority("Third");
        ThreadPriority thread4 = new ThreadPriority("Fourth");
        ThreadPriority thread5 = new ThreadPriority("Fifth");

        // set thread1 to minimum priority = 1
        thread1.setPriority(Thread.MIN_PRIORITY);

        // set thread2 to priority 2
        thread2.setPriority(2);

        // set thread3 to normal priority = 5
        thread3.setPriority(Thread.NORM_PRIORITY);

        // set thread4 to priority 8
        thread4.setPriority(8);

        // set thread5 to maximum priority = 10
        thread5.setPriority(Thread.MAX_PRIORITY);

        thread1.start();
        thread2.start();
        thread3.start();
        thread4.start();
        thread5.start();
    }

    @Override
    public void run() {
        System.out.println("Running [" + threadName + "]");
        for (int i = 1; i <= 10; i++) {
            System.out.println("[" + threadName + "] => " + i);

            try {
                Thread.sleep(500);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}