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Object Oriented Programming Articles
Page 495 of 589
How to implement a program to count the number in Java?
The program uses a JLabel to hold a count label, a JTextField component to hold the number count, JButton component to create add, remove and reset buttons. When we click the add button, the count in the JTextField will get incremented by '1' and by clicking the remove button the count will be decremented by '1'. If we click the Reset button, it will reset the count to '0'.Exampleimport java.awt.*; import java.awt.event.*; import javax.swing.*; public class CounterTest extends JFrame implements ActionListener { private JLabel label; private JTextField text; private JButton addBtn, ...
Read MoreHow many types of JDialog boxes can be created in Java?
A JDialog is a subclass of Dialog class and it does not hold minimize and maximize buttons at the top right corner of the window. We can create two types of JDialog boxes.in JavaModal DialogNon-Modal DialogModal JDialogIn Java, When a modal dialog window is active, all the user inputs are directed to it and the other parts of the application are inaccessible until this model dialog is closed.Non-Modal JDialogIn Java, When a non-modal dialog window is active, the other parts of the application are still accessible as normal and inputs can be directed to them, while this non-modal dialog window ...
Read MoreHow can we implement line wrap and word wrap text inside a JTextArea in Java?
A JTextArea is a multi-line text component to display text or allow the user to enter the text and it will generate a CaretListener interface when we are trying to implement the functionality of the JTextArea component. A JTextArea class inherits the JTextComponent class in Java.In the below example, we can implement a JTextArea class with a user can select either word wrap or line wrap checkboxes using the ItemListener interface.Exampleimport javax.swing.*; import java.awt.*; import java.awt.event.*; public class JTextAreaTest { public static void main(String[] args ) { EventQueue.invokeLater(new Runnable() { @Override public void run() { ...
Read MoreWhat is the importance of the GridBagConstraints class in Java?
A GridBagLayout is a very flexible layout manager that allows us to position the components relative to one another using constraints. Each GridBagLayout uses a dynamic rectangular grid of cells with each component occupying one or more cells called its display area. Each component managed by a GridBagLayout is associated with a GridBagConstraints instance that specifies how the component is laid out within its display area. GridBagConstraintsWe can customize a GridBagConstraints object by setting one or more of its public instance variables. These variables specify the component location, size, growth factor, anchor, inset, filling, and padding.gridx: An int value that specifies the leftmost cell that the ...
Read MoreWhat is the importance of SwingUtilities class in Java?
In Java, after swing components displayed on the screen, they can be operated by only one thread called Event Handling Thread. We can write our code in a separate block and can give this block reference to Event Handling thread. The SwingUtilities class has two important static methods, invokeAndWait() and invokeLater() to use to put references to blocks of code onto the event queue.Syntaxpublic static void invokeAndWait(Runnable doRun) throws InterruptedException, InvocationTargetException public static void invokeLater(Runnable doRun)The parameter doRun is a reference to an instance of Runnable interface. In this case, the Runnable interface will not be passed to the constructor of a Thread. The Runnable interface is simply ...
Read MoreWhat are the differences between JFrame and JDialog in Java?
JFrameThe components added to the frame are referred to as its contents, these are managed by the contentPane. To add a component to a JFrame, we must use its contentPane instead.A JFrame contains a window with title, border, (optional) menu bar and user-specified components.A JFrame can be moved, resized, iconified and it is not a subclass of JComponent.By default, JFrame is displayed in the upper-left corner of the screen. To display a frame at a specified location, we can use the setLocation(x, y) method in the JFrame class.Exampleimport java.awt.*; import java.awt.event.*; import javax.swing.*; public class JFrameDemo { public static void main(String s[]) { ...
Read MoreWhy AWT components are heavy-weight while Swing components are light-weight in Java?
AWT stands for Abstract Window ToolKit and it supports Java GUI programming. It is a portable GUI library for Stand-alone Java applications/applets. The AWT provides the connection between our application and the native GUI while Java Swing implements a set of GUI components that build on AWT technology and it can provide a pluggable look and feel. Java Swing is implemented entirely in the Java programming language.First of all, by a heavy-weight, it means the code will take comparatively more time to load and it will consume more System resources. AWT is considered to be heavy-weight because its components are dependent ...
Read MoreWhy the constructor name is same as the class name in Java?
Every class object is created using the same new keyword, so it must have information about the class to which it must create an object. For this reason, the constructor name should be the same as the class name.Exampleclass MyConstructor{ public MyConstructor() { System.out.println("The constructor name should be same as the class name"); } public static void main(String args[]){ MyConstructor mc = new MyConstructor(); } }In the above program, the constructor name should be the same as the class name (MyConstructor).OutputThe constructor name should be same as the class name
Read MoreScope and lifetime of variables in Java?
Instance VariablesA variable which is declared inside a class and outside all the methods and blocks is an instance variable. The general scope of an instance variable is throughout the class except in static methods. The lifetime of an instance variable is until the object stays in memory.Class VariablesA variable which is declared inside a class, outside all the blocks and is marked static is known as a class variable. The general scope of a class variable is throughout the class and the lifetime of a class variable is until the end of the program or as long as the ...
Read MoreDifference between Object level lock and Class level lock in Java
In multithreading environment, two or more threads can access the shared resources simultaneously which can lead the inconsistent behavior of the system. Java uses concept of locks to restrict concurrent access of shared resources or objects. Locks can be applied at two levels −Object Level Locks − It can be used when you want non-static method or non-static block of the code should be accessed by only one thread.Class Level locks − It can be used when we want to prevent multiple threads to enter the synchronized block in any of all available instances on runtime. It should always be ...
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