1.Interfaces provide a form of multiple inheritance. A class can extend only one other class. 2.Interfaces are limited to public methods and constants with no implementation. Abstract classes can have a partial implementation, protected parts,... Read More

Wrapped classes are classes that allow primitive types to be accessed as objects Read More

NO, because main is a static method. A static method can't be overridden in Java. Read More

java does not support multiple inheritance because different classes may have different variable with same name that may be be contradicted and can cause confusions resulting in errors. or Java absolutely support multiple inheritance in terms... Read More

Methods declared with the keyword static as modifier are called static methods or class methods. They are so called because they affect a class as a whole, not a particular instance of the class. Static methods are always invoked without reference to... Read More

Inheritance, Overloading and Overriding are used to achieve Polymorphism in java). Polymorphism manifests itself in Java in the form of multiple methods having the same name. * In some cases, multiple methods have the same name, but different formal... Read More

A class containing abstract method is called Abstract class. An Abstract class can't be instantiated. Example of Abstract class: abstract class testAbstractClass { protected String myString; public String getMyString() { return... Read More

* Constructors use this to refer to another constructor in the same class with a different parameter list. * Constructors use super to invoke the superclass's constructor. If a constructor uses super, it must use it in the first line; otherwise... Read More

The final modifier keyword makes that the programmer cannot change the value anymore. The actual meaning depends on whether it is applied to a class, a variable, or a method. * final Classes- A final class cannot have subclasses. * final... Read More

Yes, derived classes still can override the overloaded methods. Polymorphism can still happen. Compiler will not binding the method calls since it is overloaded, because it might be overridden now or in the future. Read More

Binding refers to the linking of a procedure call to the code to be executed in response to the call. Dynamic binding (also known as late binding) means that the code associated with a given procedure call is not known until the time of the call at... Read More

Class Methods Instance Methods Class methods are methods which are declared as static. The method can be called without creating an instance of the class Instance methods on the other hand require an instance of the class to exist before they can be... Read More

Yes, other nonabstract methods can access a method that you declare as abstract. Read More

Variables that have only one copy per class are known as static variables. They are not attached to a particular instance of a class but rather belong to a class as a whole. They are declared by using the static keyword as a modifier. static type... Read More

Interfaces may have member variables, but these are implicitly public, static, and final- in other words, interfaces can declare only constants, not instance variables that are available to all implementations and may be used as key references for... Read More

Whenever the exception occurs in Java, we need a way to tell the JVM what code to execute. To do this, we use the try and catch keywords. The try is used to define a block of code in which exceptions may occur. One or more catch clauses match a... Read More

throws: Used in a method's signature if a method is capable of causing an exception that it does not handle, so that callers of the method can guard themselves against that exception. If a method is declared as throwing a particular class of... Read More

Variables declared within a method are ?local? variables. Variables declared within the class i.e not within any methods are ?member? variables (global variables). Variables declared within the class i.e not within any methods and are defined as ... Read More

An array is indexed fixed number of homogeneous elements. where as in Array List you can create any number of objects with any type. Read More

No, constructor cannot be inherited, though a derived class can call the base class constructor. Read More

Static variables and methods are instantiated only once per class. In other words they are class variables, not instance variables. If you change the value of a static variable in a particular object, the value of that variable changes for all... Read More

The finally block encloses code that is always executed at some point after the try block, whether an exception was thrown or not. This is right place to close files, release your network sockets, connections, and perform any other cleanup your code... Read More

Wrapper class is wrapper around a primitive data type. An instance of a wrapper class contains, or wraps, a primitive value of the corresponding type. Read More

Synchronization is a process of controlling the access of shared resources by the multiple threads in such a manner that only one thread can access one resource at a time. In non synchronized multithreaded application, it is possible for one thread... Read More

* Abstraction focuses on the outside view of an object (i.e. the interface) Encapsulation (information hiding) prevents clients from seeing it?s inside view, where the behavior of the abstraction is implemented. * Abstraction solves the problem in... Read More

Two ways to create threads 1. By creating thread class class class name extends Thread { } 2.By converting class to thread ie using Runnable interface Read More

The Collection API is a set of classes and interfaces that support operation on collections of objects. These classes and interfaces are more flexible, more powerful, and more regular than the vectors, arrays, and hashtables if effectively replaces. Read More

Encapsulation is a technique used for hiding the properties and behaviors of an object and allowing outside access only as appropriate. It prevents other objects from directly altering or accessing the properties or methods of the encapsulated object... Read More

Polymorphism is briefly described as "one interface, many implementations." Polymorphism is a characteristic of being able to assign a different meaning or usage to something in different contexts - specifically, to allow an entity such as a variable... Read More

To invoke a superclass method that has been overridden in a subclass, you must either call the method directly through a superclass instance, or use the super prefix in the subclass itself. From the point of the view of the subclass, the super prefix... Read More

There is no multiple inheritance in java,we can't extends more than one class at a time,so interface is a way to implement multiple inheritance in java, and from design point view when we have some class specific behaviours we can put... Read More

You can?t instantiate an interface directly, but you can instantiate a class that implements an interface. Read More

A static variable is associated with the class as a whole rather than with specific instances of a class. Non-static variables take on unique values with each object instance. Read More

Yes, we can have the try block without catch block, but finally block should follow the try block. Note: It is not valid to use a try clause without either a catch clause or a finally clause. Read More

Java methods are similar to functions or procedures in other programming languages. Every Java program must have one main() method. Here is the main() method from a Java program which prints "Hello World": public static void main ... Read More

Transient variable can't be serialize. For example if a variable is declared as transient in a Serializable class and the class is written to an ObjectStream, the value of the variable can't be written to the stream instead when the class... Read More

Synchronized blocks place locks for shorter periods than synchronized methods. Read More

Marker interfaces are those which do not declare any required methods, but signify their compatibility with certain operations. The java.io.Serializable interface and Cloneable are typical marker interfaces. These do not contain any methods, but... Read More

All objects in Java are inherited from same base class called 'Object'.In Java all objects have common interface to implement and it makes implementaion of Garbage collector lot easier in Java.The necessary implementaion is provided in base... Read More

Yes, it is always necessary to create an object implementation for an interface. Interfaces cannot be instantiated in their own right, so you must write a class that implements the interface and fulfill all the methods defined in it. Read More

Use Interfaces when? * You see that something in your design will change frequently. * If various implementations only share method signatures then it is better to use Interfaces. * you need some classes to use some methods which you don't... Read More

Throwable", the parent class of all exception related classes. Read More

In Java Interface defines the methods but does not implement them. Interface can include constants. A class that implements the interfaces is bound to implement all the methods defined in Interface. Read More

User defined Exceptions are the separate Exception classes defined by the user for specific purposed. An user defined can created by simply sub-classing it to the Exception class. This allows custom exceptions to be generated (using throw) and caught... Read More

There are two types of polymorphism one is Compile time polymorphism and the other is run time polymorphism. Compile time polymorphism is method overloading. Runtime time polymorphism is done using inheritance and interface. Note: From a practical... Read More

To prevent a specific method from being overridden in a subclass, use the final modifier on the method declaration, which means "this is the final implementation of this method", the end of its inheritance hierarchy. public final void exampleMethod(... Read More

Early binding is nothing but declaring the Object of specific type but with this kind of object its cant be used to hold any other type of the Object/class. Read More

Garbage collection is one of the most important feature of Java. Garbage collection is also called automatic memory management as JVM automatically removes the unused variables/objects (value is null) from the memory. User program cann't... Read More

Inheritance is the process by which one object acquires the properties of another object. Read More

super is a keyword which is used to access the method or member variables from the superclass. If a method hides one of the member variables in its superclass, the method can refer to the hidden variable through the use of the super keyword. In the... Read More

Encapsulation is a process of binding or wrapping the data and the codes that operates on the data into a single entity. This keeps the data safe from outside interface and misuse. One way to think about encapsulation is as a protective wrapper that... Read More

if a class contains abstract method,that class must be declared as a abstract class. Abstract methods contains only declarations. it does not contain objects. Read More

If a class defined by the code does not have any constructor, compiler will automatically provide one no-parameter-constructor (default-constructor) for the class in the byte code. The access modifier (public/private/etc.) of the default constructor... Read More

Static block which exactly executed exactly once when the class is first loaded into JVM. Before going to the main method the static block will execute. Read More

An abstract class can never be instantiated. Its sole purpose is to be extended (subclassed). Read More

Yes, there can be an abstract class without abstract methods. Read More

An Error indicates that a non-recoverable condition has occurred that should not be caught. Error, a subclass of Throwable, is intended for drastic problems, such as OutOfMemoryError, which would be reported by the JVM itself. Read More

A unchecked exception classes which are the error classes (Error and its subclasses) are exempted from compile-time checking because they can occur at many points in the program and recovery from them is difficult or impossible. A program declaring... Read More

If there is a return statement in the try block, the finally block executes right after the return statement encountered, and before the return executes. Read More

The meaning of Polymorphism is something like one name many forms. Polymorphism enables one entity to be used as general category for different types of actions. The specific action is determined by the exact nature of the situation. The concept of... Read More

Method overriding occurs when sub class declares a method that has the same type arguments as a method declared by one of its superclass. The key benefit of overriding is the ability to define behavior that?s specific to a particular subclass type.... Read More

When we create a number of objects of the same class, then each object will share a common copy of variables. That means that there is only one copy per class, no matter how many objects are created from it. Class variables or static variables are... Read More

Throw:it is used to raise exception explicitly that means it is use when a user defined exception is raised. Throws:if a method is capable of throwing an exception but it does not handle the exception that must be specified by using "throws"... Read More

An exception is an event, which occurs during the execution of a program, that disrupts the normal flow of the program's instructions. Read More

The runtime exception classes (RuntimeException and its subclasses) are exempted from compile-time checking because, in the judgment of the designers of the Java programming language, having to declare such exceptions would not aid significantly in... Read More

There are two ways to handle exceptions: * Wrapping the desired code in a try block followed by a catch block to catch the exceptions. * List the desired exceptions in the throws clause of the method and let the caller of the method handle those... Read More

There are four main principals of oops which are called Polymorphism, Inheritance and Encapsulation and abstraction. Read More

In Java, runtime polymorphism or dynamic method dispatch is a process in which a call to an overridden method is resolved at runtime rather than at compile-time. In this process, an overridden method is called through the reference variable of a... Read More

Overloaded Method Overridden Method Arguments Must change Must not change Return type Can change Can?t change except for covariant returns Exceptions Can change Can reduce or eliminate. Must not throw new or... Read More

Polymorphism exists in three distinct forms in Java: 1.Method overloading 2. Method overriding through inheritance 3. Method overriding through the Java interface Read More

An interface is a description of a set of methods that conforming implementing classes must have. Note: * You can?t mark an interface as final. * Interface variables must be static. * An Interface cannot extend anything but another interfaces. ... Read More

Abstract Class Interfaces An abstract class can provide complete, default code and/or just the details that have to be overridden. An interface cannot provide any code at all,just the signature. In case of abstract class, a class may extend only... Read More

Java offers four access specifiers, listed below in decreasing accessibility: * Public- public classes, methods, and fields can be accessed from everywhere. * Protected- protected methods and fields can only be accessed within the same class to... Read More

By extending the Exception class or one of its subclasses. Example: class MyException extends Exception { public MyException() { super(); } public MyException(String s) { super(s); } } Read More

Neither Abstract classes or Interface can be instantiated. Read More

There are four principle concepts upon which object oriented design and programming rest. They are: * Abstraction * Polymorphism * Inheritance * Encapsulation (i.e. easily remembered as A-PIE). Read More

Method Overloading means to have two or more methods with same name in the same class with different arguments. The benefit of method overloading is that it allows you to implement methods that support the same semantic operation but differ by... Read More

One of the techniques in object-oriented programming is encapsulation. It concerns the hiding of data in a class and making this class available only through methods. Java allows you to control access to classes, methods, and fields via so-called... Read More

Abstraction refers to the act of representing essential features without including the background details or explanations. Read More

You can't force GC, but could request it by calling System.gc(). JVM does not guarantee that GC will be started immediately. Read More

C++ has proven by example that operator overloading makes code almost impossible to maintain. In fact there very nearly wasn?t even method overloading in Java, but it was thought that this was too useful for some very basic methods like print(). Note... Read More

* Inheritance is the process by which objects of one class acquire the properties of objects of another class. * A class that is inherited is called a superclass. * The class that does the inheriting is called a subclass. * Inheritance is done by... Read More

Constructors Methods Purpose Create an instance of a class Group Java statements Modifiers Cannot be abstract, final, native, static, or synchronized Can be abstract, final, native, static, or synchronized Return Type ... Read More

There are two types of exceptions in Java, unchecked exceptions and checked exceptions. * Checked exceptions: A checked exception is some subclass of Exception (or Exception itself), excluding class RuntimeException and its subclasses. Each method... Read More

This keyword indicates that the value of this member variable does not have to be serialized with the object. When the class will be de-serialized, this variable will be initialized with a default value of its data type (i.e. zero for integers). Read More

Only public and abstract modifiers are allowed for methods in interfaces. Read More

Abstract classes are classes that contain one or more abstract methods. An abstract method is a method that is declared, but contains no implementation. Note: * If even a single method is abstract, the whole class must be declared abstract. *... Read More

* A constructor is a special method whose task is to initialize the object of its class. * It is special because its name is the same as the class name. * They do not have return types, not even void and therefore they cannot return values. * They... Read More

There are two reasons for marking a method as final: * Disallowing subclasses to change the meaning of the method. * Increasing efficiency by allowing the compiler to turn calls to the method into inline Java code. Read More

Exception handling provides the following advantages over "traditional" error management techniques: * Separating Error Handling Code from "Regular" Code. * Propagating Errors Up the Call Stack. * Grouping Error Types and Error Differentiation. ... Read More