Can main class be private in java

You asked: Why is main not private in Java?

Why is main method public in Java? We know that anyone can access/invoke a method having public access specifier. The main method is public in Java because it has to be invoked by the JVM. So, if main() is not public in Java, the JVM won’t call it.

Can main () function in Java be made private?

Yes, we can declare the main method as private in Java. It compiles successfully without any errors but at the runtime, it says that the main method is not public.

Can main class be public in Java?

Java main() method. public: It is an access specifier. We should use a public keyword before the main() method so that JVM can identify the execution point of the program.

Why the main method class is public?

The main method in Java is public so that it’s visible to every other class, even which are not part of its package. if it’s not public JVM classes might not able to access it. 2. The main method is static in Java so that it can be called without creating any instance.

Can we use this () and super () in a constructor?

both this() and super() can not be used together in constructor. this() is used to call default constructor of same class.it should be first statement inside constructor. super() is used to call default constructor of base class.it should be first statement inside constructor.

Is Main a keyword in java?

Main is not a keyword in Java. When you try to execute a java code using “java” command, the runtime will load the public class that you are trying to execute and then call the main method defined in the class. The runtime knows that “main” is the method to look for as it is designed that way.

Can main method be final?

The short answer is Yes. You can declare main method as final. without any compile error.

What happens if the main () method is declared as private?

But if you declare main method as private, you would not be able to execute the class as a standalone java program. Any java class that needs to be executed as a standalone file needs to have a main method that is public, static and returns a void.

Can we override static method?

Static methods cannot be overridden because they are not dispatched on the object instance at runtime. The compiler decides which method gets called. Static methods can be overloaded (meaning that you can have the same method name for several methods as long as they have different parameter types).

Can we have 2 main methods in Java?

A class can define multiple methods with the name main. The signature of these methods does not match the signature of the main method. These other methods with different signatures are not considered the “main” method. Yes it is possible to have two main() in the same program.

Why Main is static in Java?

The main() method is static so that JVM can invoke it without instantiating the class. This also saves the unnecessary wastage of memory which would have been used by the object declared only for calling the main() method by the JVM.

Should the main class be public?

The main method must be declared public, static and void in Java otherwise, JVM will not able to run Java program. 2. JVM throws NoSuchMethodException:main if it doesn’t find the main method of predefined signature in class which is provided to Java command. … The main method is an entry point for any Core Java program.

Can we execute a program without main?

Yes You can compile and execute without main method By using static block.

Is overriding possible in java?

In Java, methods are virtual by default. We can have multilevel method-overriding. Overriding vs Overloading : … Overriding is about same method, same signature but different classes connected through inheritance.

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Can we declare main() method as private or protected or with no access modifier in java?

Java provides various access specifiers namely private, public and protected etc.

• The Private modifier restricts the access of members from outside the class. A class and interface cannot be public.
• The Public access modifier can be associated with class, method, constructor, interface, etc. public can be accessed from any other class.
• The protected access modifier can be associated with variables, methods, and constructors, which are declared protected in a superclass can be accessed only by the subclasses in other package or any class within the package of the protected members’ class.
• The default access modifier does not have keyword a variable or method declared without any access control modifier is available to any other class in the same package.

Therefore, if you declare a method public it can be accessed from anywhere outside the class. As we know that JVM accesses/invokes the main method directly if the main method is public JVM can invoke it from anywhere.

Declaring the main method private or, protected

You can define the main method in your program without private, protected or, default (none) modifier, the program gets compiled without compilation errors.

But, at the time of execution JVM does not consider this 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 main(String[] args)

If such a method is not found, a run time error is generated.

Example

In the following Java program, the class Sample contains the main method which is public.

Output

On executing, this program generates the following error.

Error: Main method not found in class Sample, please define the main method as: public static void main(String[] args) or a JavaFX application class must extend javafx.application.Application

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Can we declare a top level class as protected or private in Java?

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.

Syntax

// A top level class public class TopLevelClassTest < // Class body >

• If a top-level class is declared as private the compiler will complain that the modifier private is not allowed here. This means that a top-level class cannot be a private, the same can be applied to protected access specifier also.
• Protected means that the member can be accessed by any class in the same package and by subclasses even if they are in another package.
• The top-level classes can only have public, abstract and final modifiers, and it is also possible to not define any class modifiers at all. This is called default/package accessibility.
• We can declare the inner classes as private or protected, but it is not allowed in outerclasses.
• More than one top-level class can be defined in a Java source file, but there can be at most one public top-level class declaration. The file name must match the name of the public class.

Declare the class as Protected

Example

protected class ProtectedClassTest < int i = 10; void show() < System.out.println("Declare top-level class as protected"); >> public class Test < public static void main(String args[]) < ProtectedClassTest pc = new ProtectedClassTest(); System.out.println(pc.i); pc.show(); System.out.println("Main class declaration as public"); >>

In the above example, we can declare the class as protected, it will throw an error says that modifier protected not allowed here. So the above code doesn’t execute.

Output

modifier protected not allowed here

Declare the class as Private

Example

private class PrivateClassTest < int x = 20; void show() < System.out.println("Declare top-level class as private"); >> public class Test < public static void main(String args[]) < PrivateClassTest pc = new PrivateClassTest(); System.out.println(pc.x); pc.show(); System.out.println("Main class declaration as public"); >>

In the above example, we can declare the class as private, it will throw an error says that modifier private not allowed here. So the above code doesn’t execute.

Output

modifier private not allowed here

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Private class in java

Yes, we can declare a class as private but these classes can be only inner or nested classes. We can’t a top-level class as private because it would be completely useless as nothing would have access to it.

Example 1 with non inner class:

private class Main { public static void main(String[] args) { System.out.println("Inside private class"); } }

Main.java:1: error: modifier private not allowed here private class Main ^ 1 error

Main.java:1: error: modifier private not allowed here private class Main ^ 1 error

Example 2 with non inner class:

private class Show{ void display(){ System.out.println("Inside display method."); } } public class Main { public static void main(String[] args) { Show show = new Show(); show.display(); } }

Main.java:1: error: modifier private not allowed here private class Show{ ^ 1 error

Main.java:1: error: modifier private not allowed here private class Show< ^ 1 error

Example with inner class:

class Display { //Private nested or inner class private class InnerDisplay { public void display() { System.out.println("Private inner class method called"); } } void display() { System.out.println("Outer class (Display) method called"); // Access the private inner class InnerDisplay innerDisplay = new InnerDisplay(); innerDisplay.display(); } } public class Main { public static void main(String args[]) { // Create object of the outer class (Display) Display object = new Display(); // method invocation object.display(); } }

Outer class (Display) method called Private inner class method called

Outer class (Display) method called Private inner class method called

Java interview questions on access modifiers

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