Constructors are similar to methods but, They do not have any return type. The name of the constructor is same as the name of the class. Every class has a constructor. If we do not explicitly write a constructor for a class, the Java compiler builds a default constructor for that class. Each time a new object is created, at least one constructor will be invoked. A class can have more than one constructor. this() and super() are used to call constructors explicitly. Where, using this() you can call the current class’s constructor and using super() you can ... Read More

Java 8 introduces a new concept of default method implementation in interfaces. This capability is added for backward compatibility so that old interfaces can be used to leverage the lambda expression capability of Java 8. For example, ‘List’ or ‘Collection’ interfaces do not have ‘foreach’ method declaration. Thus, adding such method will simply break the collection framework implementations. Java 8 introduces default method so that List/Collection interface can have a default implementation of foreach method, and the class implementing these interfaces need not implement the same. Syntax public interface vehicle { default void print() { ... Read More

The class Component is the abstract base class for the non-menu user-interface controls of AWT. A component represents an object with graphical representation. The class Container is the superclass for the containers of AWT. The container object can contain other AWT components.

All instance methods in Java are virtual except, static methods and private methods.

The java.util.Locale class object represents a specific geographical, political, or cultural region. An operation that requires a Locale to perform its task is called locale-sensitive and uses the Locale to form information for the user. The locale is a mechanism for identifying objects, not a container for the objects themselves.

System class belongs to the package java.lang. It cannot be instantiated. A System class provides − standard output. error output streams. standard input and access to externally defined properties and environment variables. A utility method for quickly copying a portion of an array. a means of loading files and libraries. Following are the fields for java.lang.System class − static PrintStream err − This is the "standard" error output stream. static InputStream in − This is the "standard" input stream. static PrintStream out − This is the "standard" output stream.

The Callable interface is found in the package java.util.concurrent. The Callable object can return the computed result done by a thread in contrast to a runnable interface which can only run the thread. The Callable object returns a Future object which provides methods to monitor the progress of a task being executed by a thread. The future object can be used to check the status of a Callable and then retrieve the result from the Callable once the thread is done. It also provides timeout functionality.

An interface is like a reference type, similar to a class that enforces the rules that the class must implements(It is a keyword). An interface may have abstract methods i.e. methods without a definition and also constants or variables with fixed value. What is a Runnable interface in Java? If your class is intended to be executed as a thread, then you can achieve this by implementing a Runnable interface. This belongs to the java.lang package. The Runnable interface in Java is a functional interface that enables the compiled code of the class to run as a separate thread. The ... Read More

You can access the private methods of a class using java reflection package.Step1 − Instantiate the Method class of the java.lang.reflect package by passing the method name of the method which is declared private.Step2 − Set the method accessible by passing value true to the setAccessible() method.Step3 − Finally, invoke the method using the invoke() method.Exampleimport java.lang.reflect.Method; public class DemoTest {    private void sampleMethod() {       System.out.println("hello");    } } public class SampleTest {    public static void main(String args[]) throws Exception {       Class c = Class.forName("DemoTest");       Object obj ... Read More

Wan import statement in Java is used to − Import user defined classes/Interfaces Whenever you need to access a class which is not in the current package of the program you need to import that particular class using the import statement. Example In the following example we are using the Math class to find the square root of a number therefore, first of all w should import this class using the import statement. Live Demo import java.lang.Math.*; public class Sample{ public static void main(String args[]){ System.out.println(Math.sqrt(169)); ... Read More