Can a java file have more than one class

Question

What is the purpose of having more than one class in a Java file   I am new to Java   Edited  That can be achieved by creating a inner class inside a public class  right

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Yes 200    Example   class A    void methodDeclaration     System out println               class B    public static void main String   args    new A   methodDeclaration

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In general  there should be one class per file  If you organise things that way  then when you search for a class  you know you only need to search for the file with that name    The exception is when a class is best implemented using one or more small helper classes  Usually  the code is easiest to follow when those classes are present in the same file  For instance  you might need a small  tuple  wrapper class to pass some data between method calls  Another example are  task  classes implementing Runnable or Callable  They may be so small that they are best combined with the parent class creating and calling them

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If you want to implement a singleton  that is a class that runs in your program with only one instance in memory throughout the execution of the application  then one of the ways to implement a singleton is to nest a private static class inside a public class   Then the inner private class only instantiates itself when its public method to access the private instance is called   Check out this wiki article   https   en wikipedia org wiki Singleton pattern  The concept takes a while to chew on

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If you want to implement a public class  you must implement it in a file with the same name as that class  A single file can contain one public and optionally some private classes  This is useful if the classes are only used internally by the public class  Additionally the public class can also contain inner classes   Although it is fine to have one or more private classes in a single source file  I would say that is more readable to use inner and anonymous classes instead  For example one can use an anonymous class to define a Comparator class inside a public class     public static Comparator MyComparator   new Comparator         public int compare Object obj  Object anotherObj                  The Comparator class will normally require a separate file in order to be public  This way it is bundled with the class that uses it

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Yes it can but there can only be 1 public class inside any package as java compiler creates the  Class file which is of the same name as the Public class name therefore if their are more than 1 public class it would be difficult to select for compiler that what should be the name of Class file

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Yes  as many as you want   BUT  only one  public  class in every file

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Yes you can have more than one class inside a  java file  At most one of them can be public  The others are package-private  They CANNOT be private or protected  If one is public  the file must have the name of that class  Otherwise ANYTHING can be given to that file as its name    Having many classes inside one file means those classes are in the same package  So any other classes which are inside that package but not in that file can also use those classes  Moreover  when that package is imported  importing class can use them as well   For a more detailed investigation  you can visit my blog post in here

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There can only be one public class top level class in a file  The class name of that public class should be the name of the file  It can have many public inner classes     You can have many classes in a single file  The limits for various levels of class visibility in a file are as follows     Top level classes  1 public class 0 private class any number of default protected classes  Inner classes  any number of inner classes with any visibility  default  private  protected  public   Please correct me if I am wrong

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Yes You can have more than one Class in one  Java file   But You have make one of them Public   and save  java file with same name as name of public class  when you will compile that  java file than you will get Separate  class files for each class defined in  java file    Apart from this there are too many method for defining more than one class in one  java file     use concept of Inner Classes  Use Concept of Anonymous Classes

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Varies    One such example would be an anonymous classes  you ll encounter those alot when using event listeners and such

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In a  java file there can be only one public top-level class whose name is the same as the file  but there might be several public inner classes which can be exported to everyone and access the outer class s fields methods for example AlertDialog Builder modified by   public static   in AlertDialog modified by  public

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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

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Yes you can create more than one public class  but it has to be a nested class   public class first        public static void main String   args               TODO Auto-generated method stub            public class demo1                public class demo2

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Yes    java file can contain only one public class   If you want these two classes to be public they have to be put into two  java files  A java and B java

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I think it should be  there can only be one NON-STATIC top level public class per  java file   Isn t it

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A  java file is called a compilation unit  Each compilation unit may contain any number of top-level classes and interfaces  If there are no public top-level types then the compilation unit can be named anything    Multiple java   preceding package and import statements  class MyClass      interface Service            No public classes or interfaces      There can be only one public class interface in a compilation unit  The c u  must be named exactly as this public top-level type    Test java   named exactly as the public class Test public class Test         public class Operations      interface Selector            Other non-public classes interfaces  Important points about the main method - part 1 Part 2  Points regarding the number of classes and their access levels covered in part 2

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Yes  it can  However  there can only be one public top-level class per  java file  and public top-level classes must have the same name as the source file   The purpose of including multiple classes in one source file is to bundle related support functionality  internal data structures  support classes  etc  together with the main public class  Note that it is always OK not to do this--the only effect is on the readability  or not  of your code

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Besides anonymous inner classes  another use is private inner classes that implement a public interface  see this article   The outer class can access all private fields and methods of the inner class   This lets you create two tightly-coupled classes  such as a model and its view  without exposing the implementations of either   Another example is a collection and its iterators

[java] Can a java file have more than one class?

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