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Articles by Maruthi Krishna
Page 12 of 50
Can we declare an abstract method, private, protected, public or default in java?
A method which does not have body is known as abstract method. It contains only method signature with a semi colon and, an abstract keyword before it.public abstract myMethod();To use an abstract method, you need to inherit it by extending its class and provide implementation to it.Declaring an abstract method privateIf a method of a class is private, you cannot access it outside the current class, not even from the child classes of it.But, incase of an abstract method, you cannot use it from the same class, you need to override it from subclass and use.Therefore, the abstract method cannot ...
Read MoreIs it possible to assign a reference to "this" in java?
The "this" keyword in Java is used as a reference to the current object, within an instance method or a constructor. Using it, you can refer the members of a class such as constructors, variables, and methods.Assigning reference to "this"According to the definition "this" is a keyword which acts as a reference to the current object (the object from whose constructor/method you are using it), its value id is fixed. Therefore, you cannot assign a new reference value to it. Moreover, it is just a keyword, not a variable.Still, if you try to it assign a reference value to "this" it ...
Read MoreWhat happens if we call "super()" in a constructor without extending any class, in java?
A super keyword is a reference of the superclass object in Java. Using this, you can invoke the instance methods constructors and, variables, of a superclass.Calling the constructor of a superclassYou can call the constructor of a superclass from the subclass’s constructor.ExampleConsider the following example, it has two classes SuperClass class and SubClass where the SubClass extends the SuperClass. The superclass has a parameterized constructor, we are invoking it from the subclass using the "super" keyword.class SuperClass{ SuperClass(int data){ System.out.println("Superclass's constructor: "+data); } } public class SubClass extends SuperClass{ SubClass(int data) { super(data); ...
Read MoreCan we call Superclass’s static method from subclass in Java?
A static method is the one which you can call without instantiating the class. If you want to call a static method of the superclass, you can call it directly using the class name.Examplepublic class Sample{ public static void display(){ System.out.println("This is the static method........"); } public static void main(String args[]){ Sample.display(); } }OutputThis is the static method........It also works, if you call a static method using an instance. But, it is not recommended.public class Sample{ public static void display(){ System.out.println("This is the static method........"); ...
Read MoreDoes main() method accept arguments other than string array, in java?
The public static void main() method accepts an array of values of the type String Java from the user.public class{ public static void main(String[] args){ } }You can pass them at the time of execution right after the class name separated with spaces as −java ClassName 10 20 30And, in the program (from the main method) you can extract these values from the String array and use.ExampleFor example, you can use command line arguments to pass a and b in the above program as −public class Sample { public static void main(String[] args){ int ...
Read MoreCan we change return type of main() method in java?
The public static void main() method is the entry point of the Java program. Whenever you execute a program in Java, the JVM searches for the main method and starts executing from it.You can write the main method in your program with return type other than void, the program gets compiled without compilation errors. But, at the time of execution JVM does not consider this new method (with return type other than void) as the entry point of the program.It searches for the main method which is public, static, with return type void, and a String array as an argument.public static int ...
Read MoreIs it possible to use this keyword in static context in java?
A static method or, block belongs to the class and these will be loaded into the memory along with the class. You can invoke static methods without creating an object. (using the class name as reference).Whereas "this" in Java acts as a reference to the current object. But static contexts(methods and blocks) doesn't have any instance they belong to the class.In a simple sense, to use “this” the method should be invoked by an object, which is not always necessary with static methods.Therefore, you cannot use this keyword from a static method.ExampleIn the following Java program, the class ThisExample contains a private ...
Read MoreWhat are defender methods or virtual methods in Java?
The default methods in an interface in Java are also known as defender methods or, virtual methods.The defender/virtual methods are those that will have a default implementation in an interface. You can define defender/virtual methods using the default keyword as −default void display() { System.out.println("This is a default method"); }There is no need to implement these defender/virtual methods in the implementing classes you can call them directly.If you have an interface which is implemented by some classes and if you want to add a new method int it.Then, you need to implement this newly added method in all the ...
Read MoreCan interfaces have Static methods in Java?
An interface in Java is similar to class but, it contains only abstract methods and fields which are final and static.A static method is declared using the static keyword and it will be loaded into the memory along with the class. You can access static methods using class name without instantiation.Static methods in an interface since java8Since Java8 you can have static methods in an interface (with body). You need to call them using the name of the interface, just like static methods of a class.ExampleIn the following example, we are defining a static method in an interface and accessing ...
Read MoreCan we change an exception of a method with throws clause from unchecked to checked while overriding it in java?
A checked exception is an exception that occurs at the compile time, these are also called as compile time exceptions. These exceptions cannot simply be ignored at the time of compilation; the programmer should take care of (handle) these exceptions.An unchecked exception is an exception that occurs at the time of execution. These are also called as Runtime Exceptions. These include programming bugs, such as logic errors or improper use of an API. Runtime exceptions are ignored at the time of compilation.Unchecked to checkedWhen a method in superclass throws an unchecked exception the method the subclass method overriding cannot throw ...
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