How do I calculate the length of hypotenuse?

By Wayan in Core API, Math 0 Comment

Hypot is a mathematical function defined to calculate the length of the hypotenuse of a right-angle triangle. It was designed to avoid errors arising due to limited-precision calculations performed on computers.

From: Wikipedia

The Math.hypot(double x, double y) return the sqrt(x2+ y2) without intermediate overflow or underflow. The result will be same with this calculation Math.sqrt(Math.pow(x, 2) + Math.pow(y, 2)).

package org.kodejava.math;

public class HypotExample {
    public static void main(String[] args) {
        double number1 = 3.0d;
        double number2 = 5.0d;

        // calculate square root of total value of
        // number1 ^ 2 + number2 ^ 2
        double sqr = Math.hypot(number1, number2);

        System.out.println("Total value = " +
                (Math.pow(number1, 2) + Math.pow(number2, 2)));
        System.out.println("Square root = " + sqr);
    }
}

How do I calculate exponential function?

By Wayan in Core API, Math 1 Comment

In mathematics, the exponential function is the function ex, where e is the number (approximately 2.718281828) such that the function ex equals its own derivative. The function f(x) = ex at the point x = 0 is equal to 1.

package org.kodejava.math;

public class ExponentExample {

    public static void main(String[] args) {
        double x = 0.0d;

        // calculates e raised to the power of x (e^x)
        double fx = Math.exp(x);

        // calculates e raised to the power of x minus 1 (e^x - 1)
        double fxm1 = Math.expm1(x);

        System.out.println("fx   = " + fx);
        System.out.println("fxm1 = " + fxm1);
    }
}

How do I use the “this” keyword in Java?

By Wayan in Basic, Core API 0 Comment

Every instance method has a variable with the name this that refers to the current object for which the method is being called. You can refer to any member of the current object from within an instance method or a constructor by using this keyword.

Each time an instance method is called, the this variable is set to reference the particular class object to which it is being applied. The code in the method will then relate to the specific members of the object referred to by this keyword.

package org.kodejava.basic;

public class RemoteControl {
    private String channelName;
    private int channelNum;
    private int minVolume;
    private int maxVolume;

    RemoteControl() {
    }

    RemoteControl(String channelName, int channelNum) {
        // use "this" keyword to call another constructor in the 
        // same class
        this(channelName, channelNum, 0, 0);
    }

    RemoteControl(String channelName, int channelNum, int minVol, int maxVol) {
        this.channelName = channelName;
        this.channelNum = channelNum;
        this.minVolume = minVol;
        this.maxVolume = maxVol;
    }

    public static void main(String[] args) {
        RemoteControl remote = new RemoteControl("ATV", 10);

        // when the following line is executed, the variable in
        // changeVolume() is referring to remote object.
        remote.changeVolume(0, 25);
    }

    public void changeVolume(int x, int y) {
        this.minVolume = x;
        this.maxVolume = y;
    }
}

How do I use the “return” keyword in Java?

By Wayan in Basic, Core API 5 Comments

The return keyword is used to return from a method when its execution is complete. When a return statement is reached in a method, the program returns to the code that invoked it.

A method can return a value or reference type or does not return a value. If a method does not return a value, the method must be declared void and it doesn’t need to contain a return statement.

If a method declare to return a value, then it must use the return statement within the body of method. The data type of the return value must match the method’s declared return type.

package org.kodejava.basic;

public class ReturnDemo {

    public static void main(String[] args) {
        int z = ReturnDemo.calculate(2, 3);
        System.out.println("z = " + z);

        Dog dog = new Dog("Spaniel", "Doggie");
        System.out.println(dog.getDog());
    }

    public static int calculate(int x, int y) {
        // return an int type value
        return x + y;
    }

    public void print() {
        System.out.println("void method");

        // it does not need to contain a return statement, but it
        // may do so
        return;
    }

    public String getString() {
        return "return String type value";

        // try to execute a statement after return a value will
        // cause a compile-time error.
        //
        // String error = "error";
    }
}

class Dog {
    private String breed;
    private String name;

    Dog(String breed, String name) {
        this.breed = breed;
        this.name = name;
    }

    public Dog getDog() {
        // return Dog type
        return this;
    }

    public String toString() {
        return "breed: " + breed.concat("name: " + name);
    }
}

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How do I remove tabs from JTabbedPane?

By Wayan in Swing 1 Comment

To remove tabs from JTabbedPane we can use the following remove methods:

  • remove(int index) method to remove a tab at the specified index.
  • remove(Component component) method to remove a tab that has the specified child component.
  • removeAll() method to remove all tabs.
package org.kodejava.swing;

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

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

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

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

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

    private void initializeUI() {
        final JTabbedPane pane = new JTabbedPane(JTabbedPane.LEFT);
        pane.addTab("A Tab", new JPanel());
        pane.addTab("B Tab", new JPanel());

        JPanel tabPanel = new JPanel();
        pane.addTab("C Tab", tabPanel);
        pane.addTab("D Tab", new JPanel());
        pane.addTab("E Tab", new JPanel());

        // Remove the last tab from JTabbedPane
        pane.remove(pane.getTabCount() - 1);

        // Remove tab that contains a tabPanel component which is
        // the C Tab.
        pane.remove(tabPanel);

        JButton button = new JButton("Remove All Tabs");
        button.addActionListener(e -> {
            // Remove all tabs from JTabbedPane
            pane.removeAll();
        });

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

The output of the code snippet above is:

Remove Tabs from JTabbedPane

How do I assign keyboard shortcut to JTabbedPane tabs?

By Wayan in Swing 0 Comment

To assign a keyboard shortcut for accessing JTabbedPane‘s tab you can use the setMnemonicAt(int tabIndex, int mnemonic) method of the JTabbedPane class. The tabIndex parameter is a zero-based value parameter which means that the first tab is at index number 0. For the mnenomic parameter you can use constants value defined in the java.awt.event.KeyEvent class.

Here is an example in action on how to assign keyboard shortcut to JTabbedPane‘s tabs. To access the tabs you can use the ALT + A, ALT + B, ALT + C and ALT + D keyboard combination.

package org.kodejava.swing;

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

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

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

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

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

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

        JTabbedPane pane = new JTabbedPane();
        pane.addTab("A Tab", new JPanel());
        pane.addTab("B Tab", new JPanel());
        pane.addTab("C Tab", new JPanel());
        pane.addTab("D Tab", new JPanel());

        pane.setMnemonicAt(0, KeyEvent.VK_A);
        pane.setMnemonicAt(1, KeyEvent.VK_B);
        pane.setMnemonicAt(2, KeyEvent.VK_C);
        pane.setMnemonicAt(3, KeyEvent.VK_D);

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

The output of the code snippet above is:

JTabbedPane Tabs with Keyboard Shortcut

How do I assign tool tips for JTabbedPane tabs?

By Wayan in Swing 0 Comment

To set a tool tips for JTabbedPane‘s tabs you need to pass the tool tips when adding a new tab to the JTabbedPane. The addTab() method accept the following parameters: the tab’s title, image icon, a component that is going to be the content of the tabs and a string of tool tips information.

When you hover your mouse to the JTabbedPane‘s tabs the tool tips will be shown on the screen. Here is an example how you can can add tool tips the JTabbedPane‘s tabs.

package org.kodejava.swing;

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

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

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

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

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

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

        JTabbedPane pane = new JTabbedPane();
        ImageIcon tab1Icon = new ImageIcon(Objects.requireNonNull(
                this.getClass().getResource("/images/test-pass-icon.png")));
        ImageIcon tab2Icon = new ImageIcon(Objects.requireNonNull(
                this.getClass().getResource("/images/test-fail-icon.png")));
        ImageIcon tab3Icon = new ImageIcon(Objects.requireNonNull(
                this.getClass().getResource("/images/test-error-icon.png")));

        JPanel content1 = new JPanel();
        JPanel content2 = new JPanel();
        JPanel content3 = new JPanel();

        // Add tabs to the JTabbedPane. The last parameter in the
        // add tab method is the tool tips for the tabs.
        pane.addTab("Success", tab1Icon, content1, "Success Test Cases");
        pane.addTab("Fail", tab2Icon, content2, "Fail Test Cases");
        pane.addTab("Error", tab3Icon, content3, "Error Test Cases");

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

The result of the code snippet above is:

JTabbedPane Tabs’ Tool Tips Demo

How do I disable or enable tabs in JTabbedPane?

By Wayan in Swing 0 Comment

To enable or disable tabs in JTabbedPane you can use the JTabbedPane‘s setEnableAt(int index, boolean enable) method. The index is zero based, this means that the first tab is at index number 0. The enable parameter when set to true will enable the tab while setting to false will disable the tab.

package org.kodejava.swing;

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

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

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

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

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

    private void initializeUI() {
        JTabbedPane pane = new JTabbedPane();
        pane.addTab("Tabs A", new JPanel());
        pane.addTab("Tabs B", new JPanel());
        pane.addTab("Tabs C", new JPanel());
        pane.addTab("Tabs D", new JPanel());

        // Disable the first tab
        pane.setEnabledAt(0, false);

        // Disable the last tab, the pane.getTabCount() return the
        // number of tabs in the JTabbedPane. Because the index
        // start at 0 we need to subtract the count by 1.
        pane.setEnabledAt(pane.getTabCount() - 1, false);

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

Below is the screenshot result of the code snippet above:

Enable or Disable Tabs in JTabbedPane

How do I set the colors of JTabbedPane tabs?

By Wayan in Swing 0 Comment

The example below demonstrates how to change the color of the tabs in JTabbedPane component. The JTabbedPane‘s methods that you can use the change foreground and background color are:

  • setForeground(Color color) for changing the foreground color of all tabs.
  • setBackground(Color color) for changing the background color of all tabs.
  • setForegroundAt(int index, Color color) for changing foreground color for a tab at defined index.
  • setBackgroundAt(int index, Color color) for changing the background color of a tab at a defined index.
package org.kodejava.swing;

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

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

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

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

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

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

        JTabbedPane pane = new JTabbedPane();
        pane.addTab("A Tab", new JPanel());
        pane.addTab("B Tab", new JPanel());
        pane.addTab("C Tab", new JPanel());
        pane.addTab("D Tab", new JPanel());

        // Set all tabs foreground color to black.
        pane.setForeground(Color.BLACK);

        // Set different background color for all tabs in
        // JTabbedPane. The color from the first to the last
        // tab will be red, green yellow and orange.
        pane.setBackgroundAt(0, Color.RED);
        pane.setBackgroundAt(1, Color.GREEN);
        pane.setBackgroundAt(2, Color.YELLOW);
        pane.setBackgroundAt(3, Color.ORANGE);

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

The image below shows the result of the code snippet above:

JTabbedPane Tabs Color Demo

How do I add disabled icon for JTabbedPane tabs?

By Wayan in Swing 0 Comment

When adding a tabs to JTabbedPane you can define the icon for the tabs. This icon will be displayed beside the tab’s title in enable or disable state of the tabs. To make the user interface better you can also define a disabled icon for the tab. This icon will be displayed when the state of the tabs are disabled.

To assign a disabled icon for the tab use the JTabbedPane‘s setDisabledIconAt(int index, Icon icon) method. As always the index parameter is zero-based which means the first tab is at index number 0. The icon parameter is the disabled icon of your tabs.

package org.kodejava.swing;

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

public class TabbedPaneDisableIcon extends JPanel {
    private final ImageIcon[] disableIcons = {
            new ImageIcon(Objects.requireNonNull(
                    this.getClass().getResource("/images/test-pass-icon-disable.png"))),
            new ImageIcon(Objects.requireNonNull(
                    this.getClass().getResource("/images/test-fail-icon-disable.png"))),
            new ImageIcon(Objects.requireNonNull(
                    this.getClass().getResource("/images/test-error-icon-disable.png"))),
    };

    public TabbedPaneDisableIcon() {
        initializeUI();
    }

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

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

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

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

        JTabbedPane pane = new JTabbedPane();

        ImageIcon tab1Icon = new ImageIcon(Objects.requireNonNull(
                this.getClass().getResource("/images/test-pass-icon.png")));
        ImageIcon tab2Icon = new ImageIcon(Objects.requireNonNull(
                this.getClass().getResource("/images/test-fail-icon.png")));
        ImageIcon tab3Icon = new ImageIcon(Objects.requireNonNull(
                this.getClass().getResource("/images/test-error-icon.png")));
        JPanel content1 = new JPanel();
        JPanel content2 = new JPanel();
        JPanel content3 = new JPanel();

        pane.addTab("Pass", tab1Icon, content1);
        pane.addTab("Fail", tab2Icon, content2);
        pane.addTab("Error", tab3Icon, content3);

        for (int i = 0; i < pane.getTabCount(); i++) {
            pane.setDisabledIconAt(i, disableIcons[i]);
        }

        // Disable the last tab to see the disabled icon displayed.
        pane.setEnabledAt(pane.getTabCount() - 1, false);

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

The result of the code snippet above is:

Set Disabled Icon for JTabbedPane Tabs

Set Disabled Icon for JTabbedPane Tabs