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Object Oriented Programming Articles
Page 254 of 589
Can we declare an abstract method final or static 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 abstract method staticIf you declare a method in a class abstract to use it, you must override this method in the subclass. But, overriding is not possible with static methods. Therefore, an abstract method cannot be static.If you still, try to declare an abstract method static a compile time error is generated saying ...
Read MoreCan 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 MoreHow to rethrow an exception in Java?
Sometimes we may need to rethrow an exception in Java. If a catch block cannot handle the particular exception it has caught, we can rethrow the exception. The rethrow expression causes the originally thrown object to be rethrown.Because the exception has already been caught at the scope in which the rethrow expression occurs, it is rethrown out to the next enclosing try block. Therefore, it cannot be handled by catch blocks at the scope in which the rethrow expression occurred. Any catch blocks for the enclosing try block have an opportunity to catch the exception.Syntaxcatch(Exception e) { System.out.println("An exception ...
Read MoreCan a constructor throw an exception in Java?
Yes, constructors are allowed to throw an exception in Java.A Constructor is a special type of a method that is used to initialize the object and it is used to create an object of a class using the new keyword, where an object is also known as an Instance of a class. Each object of a class will have its own state (Instance variables) and access to methods of its class.Throw an Exception from a ConstructorA checked exception can be used to indicate a legitimate problem when trying to create an instance, while an unchecked exception typically indicates a bug either in the ...
Read MoreWhat is the importance of "Java.lang.Class" in Java?
The java.lang.Class is one of the most important class in Java and it can provide several utility methods like getClass(), forName() which is used to find and load a class. It can also provide methods like Class.newInstance() which is the backbone of reflection and allow us to create an instance of a class without using new() operator.Importance of java.lang.ClassInstances of the class Class represent classes, interfaces, enum and annotation in a running Java application.Whenever a java file is compiled, the compiler will insert a public, static, final field named Class of the type java.lang.Class into generated .class fileEach and every class exposes its code in the form of an ...
Read MoreHow to create an immutable class with mutable object references in Java?
Immutable objects are those objects whose states cannot be changed once initialized. Sometimes it is necessary to make an immutable class as per the requirement. For example, All primitive wrapper classes (Integer, Byte, Long, Float, Double, Character, Boolean and Short) are immutable in Java. String class is also an immutable class.To create a custom immutable class we have to do the following stepsDeclare the class as final so it can’t be extended.Make all fields private so that direct access is not allowed.Do not provide setter methods (methods that modify fields) for variables, so that it can not be set.Make all mutable ...
Read MoreCan a method local inner class access the local final variables in Java?
Yes, we can access the local final variables using the method local inner class because the final variables are stored on the heap and live as long as the method local inner class object may live.Method Local Inner ClassA local inner class instance can be delivered as an argument and retrieved from the methods and it is available inside a valid scope.The only limitation in method local inner class is that a local parameter can be executed only when it is defined as final.The method executing the local parameters can be called after the execution of the method, within which the local inner ...
Read MoreCan we write any statements between try, catch and finally blocks in Java?
No, we cannot write any statements in between try, catch and finally blocks and these blocks form one unit. The functionality of try keyword is to identify an exception object and catch that exception object and transfer the control along with the identified exception object to the catch block by suspending the execution of the try block. The functionality of the catch block is to receive the exception class object that has been sent by the try and catch that exception class object and assigns that exception class object to the reference of the corresponding exception class defined in the catch block. The finally blocks are ...
Read MoreWhat are the different types of nested classes are defined in Java?
In Java, it is possible to define a class inside another class, such classes are called Nested classes. We can use the access modifiers like private, public, protected or default for inner classes and default or public access modifiers for outer class.There are two types of nested classes are defined in Java.Static Nested ClassNon-Static Nested ClassStatic Nested ClassWe Can define an inner class as static, so such type of classes is called a static nested class.The nested class is defined with the static keyword, so this type of nested classes doesn’t share any relationship with the instance of an outer class.A static ...
Read MoreHow many types of anonymous inner classes are defined in Java?
An anonymous inner class is an inner class which is declared without any class name at all. In other words, a nameless inner class is called an anonymous inner class. Since it does not have a name, it cannot have a constructor because we know that a constructor name is the same as the class name.We can define an anonymous inner class and create its object using the new operator at the same time in one step.Syntaxnew(argument-list){ // Anonymous class body }Types of Anonymous Inner Class in JavaAnonymous inner class that extends a classAnonymous inner class that implements an interfaceAnonymous inner ...
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