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The String type is a class in Java, it is used to represent a set of characters. Strings in Java are immutable, you cannot change the value of a String once created.Since a String is immutable, if you try to reassign the value of a String. The reference of it will be pointed to the new String object leaving an unused String in the memory.Java provides StringBuffer class as a replacement of Strings in places where there is a necessity to make a lot of modifications to Strings of characters.You can modify/manipulate the contents of a StringBuffer over and over again ... Read More
To compare two objects, the Object class provides a method with name equals(), this method accepts an object and compares it with the current object.If the references of these two objects are equal, then it returns true else this method returns false.But this method returns true only if both references points to the same object. In fact, it should return true id the contents of the both objects are equal.Exampleclass Employee { private String name; private int age; Employee(String name, int age){ this.name = name; this.age = age; } } ... Read More
An interface in Java is similar to class but, it contains only abstract methods and fields which are final and static.Since Java8 static methods and default methods are introduced in interfaces.Default Methods - Unlike other abstract methods these are the methods can have a default implementation. If you have default method in an interface, it is not mandatory to override (provide body) it in the classes that are already implementing this interface.In short, you can access the default methods of an interface using the objects of the implementing classes.Exampleinterface MyInterface{ public static int num = 100; public default void ... Read More
When write a Java program/class first of all you need to compile it using the javac command as −javac [name of the class].javaIf your program gets compiled without errors, a .class file (byte code) is created with the specified name. Then you need to execute it using the java command (JVM) as −java [class name]ExampleSuppose we Have created a simple class Calculator which adds two or, three numbers in the file with name Calculator.java in the path D:\sample as −public class Calculator { int addition(int a , int b){ int result = a+b; ... Read More
Yes, the super class reference variable can hold the sub class object actually, it is widening in case of objects (Conversion of lower datatype to a higher datatype).But, using this reference you can access the members of super class only, if you try to access the sub class members a compile time error will be generated.ExampleIn the following Java example, we have two classes namely Person and Student. The Person class has two instance variables name and age and one instance method displayPerson() which displays the name and age.The Student extends the person class and in addition to the inherited ... Read More
Inheritance can be defined as the process where one (parent/super) class acquires the members (methods and fields) of another (child/sub).If two classes are related to each other with inheritance. If the super class and sub class contains same methods (same name and arguments), When we invoke this it using the sub class object, the method of the sub class will be executed. This mechanism is known as overriding.Overriding final methodsOnce you declare a method final it cannot be overridden If you try to do so, it generates a compile time error −Exampleclass Super{ public final void demo() { ... Read More
A constructor is similar to method and it is invoked at the time creating an object of the class, it is generally used to initialize the instance variables of a class. The constructors have same name as their class and, have no return type.There is no need to invoke constructors explicitly these are automatically invoked at the time of instantiation.The this keyword in Java is a reference to the object of the current class. Using it, you can refer a field, method or, constructor of a class.Therefore, if you need to invoke a constructor explicitly you can do so, using "this()".Invoking a ... Read More
A static block is a block of code with a static keyword. In general, these are used to initialize the static members of a class. JVM executes static blocks before the main method at the time loading a class.Examplepublic class MyClass { static{ System.out.println("Hello this is a static block"); } public static void main(String args[]){ System.out.println("This is main method"); } }OutputHello this is a static block This is main methodA constructor is similar to method and it is invoked at the time creating an object of the class, it is ... Read More
When a class has two or more methods by the same name but different parameters, at the time of calling, based on the parameters passed, respective method is called (or respective method body will be bonded with the calling line dynamically). This mechanism is known as method overloading.Exampleclass Test{ public int addition(int a, int b){ int result = a+b; return result; } public int addition (int a, int b, int c){ int result = a+b+c; return result; } public static void main(String args[]){ ... Read More
Inheritance is a relation between two classes where one class inherits the properties of the other class. This relation can be defined using the extends keyword as −public class A extends B{ }The class which inherits the properties is known as sub class or, child class and the class whose properties are inherited is super class or, parent class.In inheritance a copy of super class members is created in the sub class object. Therefore, using the sub class object you can access the members of the both classes.Multiple inheritanceThere are various types of inheritance available namely single, multilevel, hierarchical, multiple ... Read More