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Articles by raja
Page 3 of 38
How to center align the items of a JComboBox in Java?
In this article, we will learn to center-align the items of a JComboBox in Java. The default rendering of a JComboBox uses a JLabel for each item. JLabel's default alignment is left-justified, hence the misalignment. JComboBox A JComboBox is a subclass of the JComponent class, and it is a combination of a text field and a drop-down list from which the user can choose a value. A JComboBox can generate an ActionListener, ChangeListener, and an ItemListener when the user actions with a combo box. Center-Align the Items of a JComboBox By default, items in the JCombobox are left-aligned. We ...
Read MoreHow can we display the line numbers inside a JTextArea in Java?
In this article, we will learn to display the line numbers inside a JTextArea in Java. When using text editors or code viewers in Java Swing applications, the showing of line numbers can greatly improve the user experience. What is a JTextArea? A JTextArea is a subclass of JTextComponent and it is a multi-line text component to display the text or allow the user to enter a text. A JTextArea can generate a CaretListener interface, which can listen to caret update events. Syntax The following is the syntax for JTextArea initialization: JTextArea textArea = new JTextArea(); By default, JTextArea does ...
Read MoreHow to save the elements of a TreeSet to a file in Java?
A TreeSet is a subclass of AbstractSet class and it does not allow duplicate elements. By default, TreeSet stores the elements in an ascending order and retrieval speed of an element out of a TreeSet is faster. The TreeSet class internally uses a TreeMap to store elements. The elements in a TreeSet are sorted according to their natural ordering. We can also save the elements stored in a TreeSet to a file by using the Arrays.asList() method and pass this set as an argument to the writeObject() method of ObjectOutputStream class. Syntax public class TreeSet extends AbstractSet implements NavigableSet, Cloneable, Serializable Example import java.util.*; import java.io.*; public ...
Read MoreWhen can we use the getClass() method in Java?
The getClass() method is from Object class and it returns an instance of the Class class. When we declare a new instance of an object, it will be referring to a class. There can only be one class per JVM but multiple object referring to it. So when we get the class of two objects, they might be referring to the same class. Syntax public final Class getClass() Example class User { private int id; private String name; public User(int id, String name) { this.id = id; this.name ...
Read MoreCan we override a protected method in Java?
Yes, the protected method of a superclass can be overridden by a subclass. If the superclass method is protected, the subclass overridden method can have protected or public (but not default or private) which means the subclass overridden method can not have a weaker access specifier. Example class A { protected void protectedMethod() { System.out.println("superclass protected method"); } } class B extends A { protected void protectedMethod() { System.out.println("subclass protected method"); } } public class Test { public static void main(String args[]) { B b = new B(); b.protectedMethod(); } } Output subclass protected method
Read MoreImportance of a Locale class in Java?
A Locale class is used to perform locale operations and supply locale information to the user. A Locale is defined as a set of parameters that represents a geographical location or place where some operation occurs. The important methods of Locale class are getAvailableLocales(), getCountry(), getDefault(), getDisplayLanguage(), getDisplayCountry(), getUnicodeLocaleKeys() etc. The Locale class uses the following constructors − Locale(String L)− Initializes locale from the language code passed as an argument. Locale(String L, String C) − Initializes locale from the language, country code passed as arguments. Locale(String L, String C, String V) − Initializes locale from the language, country, variant passed as arguments. Example import java.text.SimpleDateFormat; import java.util.Locale; public ...
Read MoreHow can we implement a Custom HashSet in Java?
A HashSet implements Set interface which does not allow duplicate values. A HashSet is not synchronized and is not thread-safe. When we can add any duplicate element to a HashSet, the add() method returns false and does not allow to add a duplicate element to HashSet. Syntax public class HashSet extends AbstractSet implements Set, Cloneable, Serializable In the below example, we can implement a Custom HashSet. Example import java.util.*; public class CustomHashSetTest extends AbstractSet { private HashMap map = null; private static final Object tempObject = new Object(); public CustomHashSetTest() { map = new HashMap(); ...
Read MoreCan a \"this\" keyword be used to refer to static members in Java?
No, the "this" keyword cannot be used to refer to the static members of a class. This is because the “this” keyword points to the current object of the class and the static member does not need any object to be called. The static member of a class can be accessed directly without creating an object in Java. Example public class StaticTest { static int a = 50; static int b; static void show() { System.out.println("Inside the show() method"); b = a + 5; ...
Read MoreWhich collection classes are thread-safe in Java?
A thread-safe class is a class that guarantees the internal state of the class as well as returned values from methods, are correct while invoked concurrently from multiple threads. The collection classes that are thread-safe in Java are Stack, Vector, Properties, Hashtable, etc. Stack The Stack class in Java implements the stack data structure that is based on the principle of LIFO. So, the Stack class can support many operations such as push, pop, peek, search, empty, etc. Example import java.util.*; public class StackTest { public static void main (String[] args) { Stack stack = new Stack(); ...
Read MoreObject level lock vs Class level lock in Java?
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 ...
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