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Articles by raja
Page 20 of 38
What is the default value of a local variable in Java?
The local variables can be declared in methods, code blocks, constructors, etc in Java. When the program control enters the methods, code blocks, constructors, etc. then the local variables are created and when the program control leaves the methods, code blocks, constructors, etc. then the local variables are destroyed. The local variables do not have any default values in Java. This means that they can be declared and assigned a value before the variables are used for the first time, otherwise, the compiler throws an error.Examplepublic class LocalVariableTest { public void print() { ...
Read MoreHow can we add padding to a JTextField in Java?
A JTextField is a subclass of JTextComponent class and it is one of the most important components that allow the user to input text value in a single-line format. A JTextField class will generate an ActionListener interface when we trying to enter some input inside it. The important methods of a JTextField class are setText(), getText(), setBorder(), setEnabled(), etc. We can add padding to a JTextField using the setMargin(Insets s) of JTextComponent class.Syntaxpublic void setMargin(Insets m)Exampleimport java.awt.*; import java.awt.event.*; import javax.swing.*; public class JTextfieldPaddingTest extends JFrame { private JTextField jtf; public JTextfieldPaddingTest() { ...
Read MoreHow to set the color to alternate rows of JTable in Java?
A JTable is a subclass of JComponent class and it can be used to create a table with information displayed in multiple rows and columns. When a value is selected from a JTable, a TableModelEvent is generated, which is handled by implementing a TableModelListener interface.We can set the color to alternate rows of JTable by overriding the prepareRenderer() method of JTable class.Syntaxpublic Component prepareRenderer(TableCellRenderer renderer, int row, int column)Exampleimport java.awt.*; import java.awt.event.*; import javax.swing.*; import javax.swing.table.*; public class AlternateRowColorTableTest extends JFrame { public AlternateRowColorTableTest() { setTitle("AlternateRowColorTable Test"); ...
Read MoreWhen can a .class file get created in Java?
A Java class file has a ".class" extension and contains the Java bytecode. This class file can be executed by the Java Virtual Machine (JVM). A ".class" file is created as a result of successful compilation by the Java compiler from the ".java" file. Each class in the .java file is compiled into a separate class file if the ".java " file has more than one class.Exampleclass A { A() { System.out.println("This is class A"); } } class B { B() { ...
Read MoreHow can we check an underflow occurs in Java?
When a value is assigned to a variable that is less than the minimum allowed value for that variable, then an underflow occurs. There is no exception thrown by the JVM if an underflow occurs in Java and it is the responsibility of a programmer to handle the underflow conditions.Examplepublic class UnderlowTest { public static void main(String[] args) { int num1 = -2147483648; int num2 = -1; System.out.println("Number 1: " + num1); System.out.println("Number ...
Read MoreHow does a ClassLoader work in Java?
A Java Class is stored in the form of byte code in a .class file after it is compiled. The ClassLoader loads the class of the Java program into memory when it is required. The ClassLoader is hierarchical and so if there is a request to load a class, it is delegated to the parent class loader.The types of ClassLoader in Java are given as followsBootstrap ClassLoaderExtensions ClassLoaderSystem ClassLoaderExamplepublic class ClassLoaderTest { public static void main(String[] args) { System.out.println("class loader for this class: " + ClassLoaderTest.class.getClassLoader()); System.out.println("class loader for DNSNameService: " + sun.net.spi.nameservice.dns.DNSNameService.class.getClassLoader()); ...
Read MoreCan we have an empty catch block in Java?
Yes, we can have an empty catch block. But this is a bad practice to implement in Java.Generally, the try block has the code which is capable of producing exceptions, if anything wrong in the try block, for instance, divide by zero, file not found, etc. It will generate an exception that is caught by the catch block. The catch block catches and handles the exception. If the catch block is empty then we will have no idea what went wrong within our code.Examplepublic class EmptyCatchBlockTest { public static void main(String[] args) { try { int a ...
Read MoreHow can we disable the leaf of JTree in Java?
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 MoreHow can we remove a selected row from a JTable in Java?
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[] ...
Read MoreImportance of SerialVersionUID keyword in Java?
SerialVersionUIDThe SerialVersionUID must be declared as a private static final long variable in Java. This number is calculated by the compiler based on the state of the class and the class attributes. This is the number that will help the JVM to identify the state of an object when it reads the state of the object from a file.The SerialVersionUID can be used during deserialization to verify that the sender and receiver of a serialized object have loaded classes for that object that are compatible w.r.t serialization. If the deserialization object is different than serialization, then it can throw an ...
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