What Is The Difference Between A Static And A Non Static Inner Class?

Should static classes be inner?

An inner class, by default, has an implicit reference to an object of the outer class.

If you instantiate an object of this from the code of the outer class, this is all done for you.

As a basic rule, if the inner class has no reason to access the outer one, you should make it static by default..

Can we create a static class in Java?

The answer is YES, we can have static class in java. In java, we have static instance variables as well as static methods and also static block. Classes can also be made static in Java. In java, we can’t make Top-level (outer) class static.

What is the need to mention static before main method?

Before the main method is called, no objects are instantiated. Having the static keyword means the method can be called without creating any objects first. Because otherwise, it would need an instance of the object to be executed.

What are disadvantages of using inner classes?

Q7)What are disadvantages of using inner classes?Using inner class increases the total number of classes being used by the application. … Inner classes get limited support of ide/tools as compared to the top level classes, so working with the inner classes is sometimes annoying for the developer.

Can we make a class private?

No, we cannot declare a top-level class as private or protected. It can be either public or default (no modifier). If it does not have a modifier, it is supposed to have a default access.

What is non static inner class in Java?

A non-static nested class is a class within another class. It has access to members of the enclosing class (outer class). It is commonly known as inner class . Since the inner class exists within the outer class, you must instantiate the outer class first, in order to instantiate the inner class.

Is static inner class thread safe?

static methods and inner classes don’t have any access to the variables of their dynamic counter part, and consequently can’t use monitors/synchronize on an instance of their parent class. Of course this doesn’t mean that declaring them and using them is inherently non-thread safe.

How do you access a static inner class?

And like static class methods, a static nested class cannot refer directly to instance variables or methods defined in its enclosing class: it can use them only through an object reference. They are accessed using the enclosing class name. To instantiate an inner class, you must first instantiate the outer class.

Can inner class final?

Inner class are defined inside the body of another class (known as outer class). These classes can have access modifier or even can be marked as abstract and final. Inner classes have special relationship with outer class instances.

Can static member classes contain non static methods?

A static class has no pointer to its outer class and can therefore only refer to static fields and methods of the outer class. A static class may however itself contain non-static methods. There’s no such thing as a “static class” in Java (at least not in the way you seem to understand it).

Can an outer class access inner class members?

Yes, including the ones declared private , just as any instance method can. “A nested class is a class defined within another class. A nested class should exist only to serve its enclosing class. … though you can access the static fields of the outer class from the inner class directly by the fields names.

Which method Cannot be overridden?

A method declared final cannot be overridden. A method declared static cannot be overridden but can be re-declared. If a method cannot be inherited, then it cannot be overridden. A subclass within the same package as the instance’s superclass can override any superclass method that is not declared private or final.

What is static inner class?

A static inner class is a nested class which is a static member of the outer class. It can be accessed without instantiating the outer class, using other static members. Just like static members, a static nested class does not have access to the instance variables and methods of the outer class.

Can inner class have constructor?

Every Object (without any exceptions) is created by invoking a constructor. Here you can see that the compiler implements your inner class by declaring a final field member holding a reference to the enclosing class. … You can, though, do constructor chaining between other declared constructors of your inner class.

What is the use of static inner class?

As with class methods and variables, a static nested class is associated with its outer class. And like static class methods, a static nested class cannot refer directly to instance variables or methods defined in its enclosing class: it can use them only through an object reference.

Why is static inner class singleton thread safe?

So, Bill Pugh suggested a concept of inner static classes to use for singleton. When the singleton class is loaded, inner class is not loaded and hence doesn’t create object when loading the class. Inner class is created only when getInstance() method is called.

Is HashMap thread safe?

HashMap is non synchronized. It is not-thread safe and can’t be shared between many threads without proper synchronization code whereas Hashtable is synchronized. It is thread-safe and can be shared with many threads.

Is StringBuilder thread safe?

StringBuilder is not synchronized so that it is not thread-safe. By not being synchronized, the performance of StringBuilder can be better than StringBuffer. If we are working in a single-threaded environment, using StringBuilder instead of StringBuffer may result in increased performance.