Can I use multi Java class in a same file?
yes. you can have as many as possible classes in the java file and also you don't even need a main class in java. but for running programm main class in different java file is need to be at in same directory in the file. 3K views
How many classes should a .java file contain?
- Compile using javac Sample.java
- Now open the Sample.class file. It will looks like following.
- Now erase at least single symbol from this Sample.class file from starting of file and save it.
- Now try to run this using java Sample command and see the magic i.e. ...
How to create custom classes in Java?
Java Class Methods
- Java Class Methods. myMethod () prints a text (the action), when it is called.
- Static vs. Non-Static. ...
- Access Methods With an Object. Create a Car object named myCar. ...
- Using Multiple Classes. Like we specified in the Classes chapter, it is a good practice to create an object of a class and access it in another class.
How to implement multiple classes in Java?
Notes on Interfaces:
- It cannot be used to create objects (in the example above, it is not possible to create an "Animal" object in the MyMainClass)
- Interface methods does not have a body - the body is provided by the "implement" class
- On implementation of an interface, you must override all of its methods
- Interface methods are by default abstract and public
Can Java file has two classes?
No, while defining multiple classes in a single Java file you need to make sure that only one class among them is public. If you have more than one public classes a single file a compile-time error will be generated.Sep 10, 2019
Can a Java file extend multiple classes?
It means a class can extend only a single class at a time. Extending more than one class will lead to code execution failure. When a class extends a class, then it is called single inheritance . If a class extends more than one class, it is called multi-inheritance , which is not allowed in Java.Jul 10, 2021
Is overriding possible in Java?
Java Overriding Rules Both the superclass and the subclass must have the same method name, the same return type and the same parameter list. We cannot override the method declared as final and static .
Why we Cannot extend two classes in Java?
here the problem comes – Because D is extending both B & C so if D wants to use the same method which method would be called (the overridden method of B or the overridden method of C). Ambiguity. That's the main reason why Java doesn't support multiple inheritance.
How many public classes can you use in Java?
You can use at most one public class per one java file (COMPILATION UNIT) and unlimited number of separate package-private classes. Compilation unit must named as public class is. You also can have in your public class the unlimited number of inner classes and static nested classes. Inner classes have an intenal pointer to ...
What should a Java class name start with?
You have broken one of the most widely observed rules of Java style. Java class names should always start with an uppercase letter. You have named your class test rather than Test. So when you wrote. test.getdata (200, 100); test looks like a variable name, and that looks like a call of an instance method.
How to avoid class problems?
The simple rule to avoid the problems is: one class per file, and call the file the same thing as the class it declares.
Why do inner classes have an intenal pointer?
Inner classes have an intenal pointer to the enclosing class so they have access to its members as well as local vars. They can be anonymuous.
How many public top level classes can you have?
You can only have one public top-level class per file. So, remove the public from all but one (or all) of the classes.
Can you use a public class in Java?
It is legal code, but unnecessary. And style guides typically recommend against doing it. You can use at most one public class per one java file (COMPILATION UNIT) and unlimited number of separate package-private classes. Compilation unit must named as public class is.
Do you have to nest classes in each other?
You have to nest your classes in each other, although it is not recommended.
What is a nested class?
A nested class is one type of inner class that accesses other instance variables of an outer class. We can use any access modifiers for the nested inner class such as private, public, protected, or default.
What is non static nested class?
The non-static nested class is a class within another class and should be accessible to members of the enclosing class (out er class). This class is also known as an inner class in Java. While an inner class exists within the outer class, you must instantiate the outer class first in order to instantiate the inner class.
Can you declare only one class in Java?
You need to have any number of classes in a single Java file, but there is a restriction that you can declare only one Java class as public modifier with the main () method and declare (without public) for the remaining classes. Moreover, we have one rule in Java that your filename must be the same as your public class name.
Is an inner class static or non static?
If You define an inner class with a static keyword, such type of class is said to be a static nested class, and an inner class is also said to be a non-static nested class in Java.
Can you have two classes in a Java file?
A Java source file can have only one class declared as public, we cannot put two or more public classes together in a . java file. This is because of the restriction that the file name should be same as the name of the public class with .
Can Java files contain multiple classes?
Yes, it can. However, there can only be one public class per . java file, as public classes must have the same name as the source file. One Java file can consist of multiple classes with the restriction that only one of them can be public.
Can you have one class inside another class?
Second, Yes you can have one class inside other class, these classes are called inner classes or nested classes in JAVA. JAVA file and name of the file should be same as the name of class. Once compiled, such file produces multiple . class files for each of the classes present in the .
Can you compile a Java file with different name?
Yes, it is possible to compile a java source file with different file name but you need to make sure none of the classes defined inside are public when you compile the source file the corresponding . class files for the classes inside the source file are created.
Can you have multiple non-nested classes in Java?
We can also have multiple non-nested classes in a single file in Java.
Can you reuse a class file?
When we run our program, two .class files are created for both classes. We can reuse the .class file again without recompiling the code. In the output, we can see our code has been executed successfully.
How the compiler behave with Multiple non-nested classes
In the below example, the java program contains two classes, one class name is Computer and another is Laptop. Both classes have their own constructors and a method. In the main method, we can create an object of two classes and call their methods.
Example
public class Computer { Computer() { System.out.println("Constructor of Computer class."); } void computer_method() { System.out.println("Power gone! Shut down your PC soon..."); } public static void main(String[] args) { Computer c = new Computer(); Laptop l = new Laptop(); c.computer_method(); l.laptop_method(); } } class Laptop { Laptop() { System.out.println("Constructor of Laptop class."); } void laptop_method() { System.out.println("99% Battery available."); } }.
Output
Constructor of Computer class. Constructor of Laptop class. Power gone! Shut down your PC soon... 99% Battery available.
How the compiler behave with Nested classes
Once the main class is compiled which has several inner classes, the compiler generates separate .class files for each of the inner classes.
Example
In the above program, we have a Main class that has four inner classes Test1, Test2, Anonymous inner class 1 and Anonymous inner class 2. Once we compile this class, it will generate the following class files.
How many classes are there in Java?
A Java program may contain any number of classes. The following program comprises of two classes: Computer and Laptop, both the classes have their constructors and a method. In the main method, we create objects of two classes and call their methods.
Can you write multiple classes in a single file?
You can create as many classes as you want, but writing many classes in a single file isn't recommended, as it makes code difficult to read. Instead, you can create a separate file for every class. You can also group classes in packages for efficiently managing the development of your application.
Can you reuse a class file?
Its advantage is you can reuse your .class file somewhere in other projects without recompiling the code. In a nutshell number of .class files created are equal to the number of classes in the program. You can create as many classes as you want, but writing many classes in a single file isn't recommended, as it makes code difficult to read.
