Java Articles - Page 181 of 445

A JTree is a component that presents a hierarchical view of data. The user has the ability to expand or collapse individual sub-trees. A TreeNode interface defines the methods that must be implemented nodes of a JTree object. The DefaulMutableTreeNode class provides a default implementation of a TreeNode interface. We can disable the leaf of JTree by overriding the getTreeCellRendererComponent() method of DefaultTreeCellRenderer class.Syntaxpublic Component getTreeCellRendererComponent(JTree tree, Object value, boolean sel, boolean expanded, boolean leaf, int row, boolean hasFocus)Exampleimport java.awt.*; import javax.swing.tree.*; import javax.swing.*; public class JTreeLeafNodeDisableTest extends JFrame {    private TreeNode treeNode;    private JTree tree;    public JTreeLeafNodeDisableTest() {       setTitle("JTreeLeafNodeDisable Test");     ... Read More

In Java, a HashMap is a subclass of the AbstractMap class and is used to store key-value pairs. Each key in the map is mapped to a single value in the map, and the keys are unique.Printing Java HashMap Elements  We can insert a key only once in a map, and duplicate keys are not allowed, but the value can be mapped to multiple keys. We can add the elements using the put() method of the HashMap class and iterate over the elements using the Iterator interface. Java HashMap provides various ways to print its elements as follows: ... Read More

A JTree is a subclass of JComponent class that can be used to display the data with the hierarchical properties by adding nodes to nodes and keeps the concept of parent and child node. Each element in the tree becomes a node. The nodes are expandable and collapsible. We can implement the mouse right-click on each node of a JTree using the mouseReleased() method of MouseAdapter class and need to call show() method of JPopupMenu class to show the popup menu on the tree node.Exampleimport java.awt.*; import java.awt.event.*; import javax.swing.*; import javax.swing.tree.*; public class JTreeRightClickTest extends JFrame {    public JTreeRightClickTest() {       ... Read More

Yes, we can synchronize a run() method in Java using the synchronized keyword before this method. If this method is synchronized, only one thread can execute this on a given instance of the object at any point in time. Here is a code snippet that shows how to define the run() method as synchronized: @Override synchronized run(){ //code implementation } Here, the @Override annotation specifies that the run() method overrides a method from the Runnable interface, and synchronized is a reserved keyword in Java used to define a method or block as synchronized. Synchronization of a run() ... Read More

A JTable is a subclass of JComponent class for displaying complex data structures. A JTable component can follow the Model View Controller (MVC) design pattern for displaying the data in rows and columns. A JTable can generate TableModelListener, TableColumnModelListener, ListSelectionListener, CellEditorListener and RowSorterListener interfaces. We can remove a selected row from a JTable using the removeRow() method of the DefaultTableModel class.Syntaxpublic void removeRow(int row)Exampleimport java.awt.*; import java.awt.event.*; import javax.swing.*; import javax.swing.table.*; public class RemoveSelectedRowTest extends JFrame {    private JTable table;    private DefaultTableModel model;    private Object[][] data;    private String[] columnNames;    private JButton button;    public RemoveSelectedRowTest() {       setTitle("RemoveSelectedRow ... Read More

What is an Annotation? An annotation is like metadata that provides additional information about the code. It does not affect the code directly but provides the information so that the compiler or runtime environment can use it while executing the code. To define or use any annotation in Java, you need to specify the annotation name starting with the "@" symbol. Here is the syntax to use annotations in Java: @annotation_name Where the @ symbol specifies the annotation, and annotation_name is the name of the annotation. Following is a list of a few important annotations and their usage: ... Read More

A JList is a subclass of JComponent class and it can be used to display a list of objects that allows the user to select one or more items. A JList can generate a ListSelectiionListener interface and need to implement the abstract method valueChanged(). A DefaultListModel class provides a simple implementation of a list model, which can be used to manage items displayed by a JList control. We can add the items to a JList using the addElement() method of the DefaultListModel class, we can also add items with different fonts to JList using HTML tags like for bold style text,   for italic style ... Read More

Both Object level lock and Class level lock are used to achieve synchronization mechanisms in a multi-threaded application. Object Level Lock Every object in Java has a unique lock. If a thread wants to execute a synchronized method on a given object, first it has to get a lock of that object. Once thread got the lock then it is allowed to execute any synchronized method on that object. Once method execution completes automatically thread releases the lock. Acquiring and release lock internally is taken care of by the JVM. Object level lock is a mechanism when we want to synchronize a non-static ... Read More

Yes! we can override the start() method of the Thread class in Java. But, if we do so, we must call it using super.start(), which will create a new thread; otherwise, no new thread will be created, and the run() method will not execute in parallel for the other threads. Overriding the start() Method In Java, the start() method is used to begin (start) the execution of a new Thread. When this method is called, it invokes the run() method, which executes in parallel with other threads.  Example In the following example, we override the start() method within the subclass of ... Read More

No, we cannot call the wait() method without acquiring the lock. In Java, once the lock has been acquired then we need to call wait() method (with timeout or without timeout) on that object. If we are trying to call the wait() method without acquiring a lock, it can throw java.lang.IllegalMonitorStateException. Example public class ThreadStateTest extends Thread { public void run() { try { wait(1000); } catch(InterruptedException ie) { ie.printStackTrace(); ... Read More