This question already has answers here:
Error: class X is public should be declared in a file named X.java
(19 answers)
Closed 9 years ago.
class Blog{
public static void main(String args[]){
System.out.println("overflow");
}
}
I am saving this file with name First.java and compiling it than it is generating file with Blog.class and gives output:
overflow
If same program i am writing as given below:-
public class Blog{
public static void main(String args[]){
System.out.println("overflow");
}
}
it gives error after compiling
First.java:3: error: class Blog is public, should be declared in a file named Blog.java
If you declare a class as public then the file name and the class name should same.Otherwise you will get compile time error.
So change you file name to Blog.java from First.java.
The reported error is really clear:
class Blog is public, should be declared in a file named Blog.java
java classes always should have same name with its file name (case sensitive) with .java extension. so you should save it Blog.java
Because it is part of the Java Language Specification! You may also have a look at Managing Source and Class Files in the Java Tutorials.
From the JLS
If and only if packages are stored in a file system (§7.2), the host
system may choose to enforce the restriction that it is a compile-time
error if a type is not found in a file under a name composed of the
type name plus an extension (such as .java or .jav) if either of the
following is true:
•The type is referred to by code in other compilation units of the
package in which the type is declared.
•The type is declared public (and therefore is potentially accessible
from code in other packages).
This restriction implies that there must be at most one such type per
compilation unit. This restriction makes it easy for a Java compiler
to find a named class within a package. In practice, many programmers
choose to put each class or interface type in its own compilation
unit, whether or not it is public or is referred to by code in other
compilation units.
Related
This question already has answers here:
File name and class name different in java
(1 answer)
Can I compile a java file with a different name than the class?
(21 answers)
Closed 6 months ago.
I usually do my homework on a Java file and submit the file to complete my task, so I separate each file and contain them all in one folder. Sometimes there are two works that have the same class name, but different work. If I let two files have the same class name, they won't run properly. (I'm using vscode)
For example:
File1.java
public class File1{
public static void main(String[] args) {
...
}
}
class Fraction {...}
File2.java
public class File2{
public static void main(String[] args) {
...
}
}
class Fraction {...} //this is not the same with File1.java
Can I do anything keep two class names the same in two different files in one folder?
Do not define the same class name (whether the same script or not) in the same folder. This throws an error many times.
Largely all filenames are Operating System rules dependent.
Java source code files must be named by the main class name of the code in the file. After compiling, a file of the same name but different extension, extension of .class will be there. Dependent how the compiler command line flags are set it will simply by default overwrite any old version .class file.
type javac -h on the shell or prompt for compile command flags info.
This question already has answers here:
Why are filenames in Java the same as the public class name? [closed]
(7 answers)
Closed 4 years ago.
I just a wrote a code like this with file name b.java
public class a{
public static void main(String args[]){
System.out.println("Hii");
}
}
it gives error like this
error: class a is public, should be declared in a file named a.java
if i remove access modifier public in front of class
it is running fine.
is there a other solution to achieve i don't want to change the names of class or file name unless there is a big reason.
If so please explain me the reason. why we should give the name of file and name of the class with same name.
If you define a class as public, then class name should match the file name.
The reason we define any class as public is to make it accessible from other classes or code in other packages.
This rule of naming file name after its class name makes it easy for the compiler to find the class.
Also in JAVA, we can have only one public class in a file.
I started to learn Java couple days ago. And I have this burning question. Is empty .java file name a valid source file name?
.java
Yes, save your java file by .java then compile it by javac .java and run by java yourclassname
class X {
public static void main(String args[]) {
System.out.println("Hello World");
}
}
to compile - javac .java
to execute - java X
Yes it's working because java compiler doesn't consider it saves file name or not except our class having public specified we can save any name or empty but when ever trying to execute we must use our class name because, jvm creates byte code ourclassname.class so we using
java className
Yes Empty .java file name works, but class must not be public, it means that it must be default.
If class is public then following error occour:
D:\Testjavac>javac .java
.java:1: error: class Empty is public, should be declared in a file named Empty.
java
public class Empty
^
1 error
Yes You can have .java file withought nay name . you have to compile it by javac .java(it compile successfuly) and run it by java clasnname.(so you must provide a class name)
Yes, but don't do this often.
You can't create any classes in that file that are public or private, so any class that made use of any class defined here would have to be in the same package.
at anytime you can have only one public class in the file and if you use public class then that class name should be the file name.
It's a simple class and I am a beginner with Java.
I don't know why this code is not running and why it gives an error :
Could not find or load main class
class tuto{
public static void main(String[] args){
System.out.println("Hello World");
}
}
There are a couple things which jump out at me when I look at your question.
The first thing is that you have unresolved compiler errors. If you see that red 'x' on the Problems tab, you should fix all the errors there before trying to run anything.
The second thing is that your class name doesn't match the file name in which it is defined. For public classes the name of the class and the name of the file must match, and while your class isn't public, this is a widely followed Java convention and you will confuse people if you don't follow it.
As to your actual question, my best guess is that you have placed your class into a package and not declared it as such in your source code. If you go look at the Problems tab, it will tell you what is wrong and (often) how to fix it.
I can approximate your error message if I do the following:
In this case, I have an error over in the Problems tab complaining about the declared package.
Check to see if you have something similar:
If you do, you can right-click the error message and select "Quick Fix", and eclipse will pop up a dialog offering to add the package declaration for you:
In your code there is a compile error, that is because Syteme change it to System
Syteme.out.println("Hello World");
should be
System.out.println("Hello World");
P.S
And in Java when you have a public class in a file, then file name must be that class name. It is a must. Otherwise you will get an error.
If you have this class in a package then you must specify the package declaration first
e.g
package abc;
System.out.println not Syteme.out.println.
In Java (as somebody has already pointed) the name of the file should be of the same name of the main class within the same file.
Moreover, you should also declare an array using this syntax array_type [] array_id and not array_type array_id [].
There might be a couple of problems:
If the class is in a package, make sure you specify it. eg: package com.pak;
The class with main method always needs to be public. public class apples{}
I have found one error in my Java program:
The public type abc class must be defined in its own class
How can I resolve this error? I am using Eclipse. I am new to Java programming.
Each source file must contain only one public class. A class named ClassName should be in a file named ClassName.java, and only that class should be defined there.
Exceptions to this are anonymous and inner classes, but understanding you are a beginner to Java, that is an advanced topic. For now, keep one class per file.
Answering your addition: it is OK to inherit classes and that's totally fine. This does not matter, each class should still have its own file.
Public top-level classes (i.e. public classes which aren't nested within other classes) have to be defined in a file which matches the classname. So the code for class "Foo" must live in "Foo.java".
From the language specification, section 7.6:
When packages are stored in a file system (§7.2.1), the host system may choose to enforce the restriction that it is a compile-time error if a type is not found in a file under a name composed of the type name plus an extension (such as .java or .jav) if either of the following is true:
The type is referred to by code in other compilation units of the package in which the type is declared.
The type is declared public (and therefore is potentially accessible from code in other packages).
This rule, which doesn't have to be followed by compilers, is pretty much universally adhered to.
Ok, maybe an example will help.
In file MySuperClass.java:
public class MySuperClass {
// whatever goes here
}
public class MySubClass1 extends MySuperClass {
// compile error: public class MySubClass1 should be in MySubClass1.java
}
class MySubClass2 extends MySuperClass {
// no problem (non-public class does not have to be in a file of the same name)
}
In file MySubClass3.java:
public class MySubClass3 extends MySuperClass {
// no problem (public class in file of the same name)
}
Does that make things clearer?
A public class with the name of "abc" must be in a file called abc.java
You can create a new class an a existing file if it's private, but you should not do this.
Create one file per class.
Eclipse does that for you, if you create a new class.
For programming Java, you have to understand the construct of classes, packages and files. Even if Eclipse helps you, you have to know it for yourself. So start reading Java books or tutorials!