How do I get the exponent of exponential function?

The exponential function is f(x) = ex. The Math.getExponent() method is used to get the x value of the given parameter, in which the parameter is a result of exponential function calculation.

package org.kodejava.math;

public class GetExponent {
    public static void main(String[] args) {
        double fx = 1.0d;
        float fx1 = 1.0f;

        int x = Math.getExponent(fx);
        System.out.println("Exponent  = " + x);

        // argument in float
        int xf = Math.getExponent(fx1);
        System.out.println("Exponent1 = " + xf);
    }
}

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

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?

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 use the “this” keyword in Java?

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 assign keyboard shortcut to JTabbedPane tabs?

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