Given the following classes:
package a.b;
public class C {
public B b;
}
and, in a different file:
public class B {}
Standing in folder folder, executing
javac B.java
javac a/b/C.java -cp .
will generate B.class inside folder and will return a Symbol not found on the second command.
How (without making any modification to any of the classes B and C) can I compile C.java?
EDIT: maybe this can't be done
If you are creating both the classes in same java file then only one class has to be as declared "public" class. And the file name should be given as
public class name.java
Also your way of creating an instance of class B is incorrect. It has to be done as follows:
B b = new B( );
Make sure to compile as:
javac -d . C.java
and make sure to remove the public access modifier from class B.
Why compile them separately?
javac B.java a/b/C.java
I believe this will work fine, since javac will be able to see both of your files.
You won't even need the -cp option, since you're already telling javac about everything you need.
Related
I was trying to compile a few files in a package in java. The package name is library. Please have a look at the following details.
This is my Directory Structure:
javalearning
---library
------ParentClass.java
------ChildClass.java
I tried to compile in the following way:
current directory: javalearning
javac library/ParentClass.java //this compilation works fine
javac library/ChildClass.java //error over here
The following is the ParentClass.java:
package library;
class Parentclass{
...
}
The following is the ChildClass.java:
package library;
class ChildClass extends ParentClass{
...
}
The error is as follows:
cannot access ParentClass
bad class file: .\library\ParentClass.class
Please remove or make sure it appears in the correct sub directory of the classpath
You've got a casing issue:
class Parentclass
That's not the same as the filename ParentClass.class, nor is it the same as the class you're trying to use in ChildClass: class ChildClass extends ParentClass.
Java classnames are case-sensitive, but Windows filenames aren't. If the class had been public, the compiler would have validated that the names matched - but for non-public classes, there's no requirement for that.
The fact that you've ended up with ParentClass.class suggests that at some point it was declared as ParentClass, but then you changed the declared name and when recompiling, Windows just overwrote the content of the current file rather than effectively creating Parentclass.class.
Make sure your declared class name exactly matches the filename. You may well want to delete all your class files before recompiling, just to get out of a confusing state.
I have a class called MyClass in the file MyClass.java file (code mentioned below)
package myclass;
class MyClass {
public int add (int a, int b){
return a+b;
}
public static void main(String args[]) {
MyClass obj = new MyClass();
System.out.println(oobj.add(2, 3));
}
}
I am compiling the class with
javac MyClass.java
But I am trying to run the class using
java MyClass
or
java myclass.MyClass
I am getting the Error
Error: Could not find or load main class MyClass
But, I am able to run this program if I omit out the package name.
where am I going wrong?
Make sure that you are inside the parent directory of the package folder (the folder in which your compiled class file is), and execute the following command:
java myclass.MyClass
Below is an example file structure:
bin
-> myclass
-> MyClass.class
In the example structure above, you would have to execute the command from the "bin" directory.
Also, define the class as public and recompile the java source file.
I ran into this too. It's very frustrating for someone from other languages. The key here is, the java file has to be in the right directory depending on the package declaration.
if the java file Test1.java starts with
package com.xyz.tests;
Then the java file Test1.java needs to be in directory com/xyz/tests
You can compile and run as
javac com/xyz/tests/Test1.java
java com/xyz/tests/Test1
Good luck.
You Need To Compile The Class using :
javac -d ./myclass
I get my example to run by
java <package>.<class>
From parent directory of package
I have a package called "test" and in that have a public class that contains the main method in a file called ABC.java.
package test;
public class ABC{
public static void main(String[] args) {
new T1();
}
}
In that same package "test" I have two default classes T1 and T2 in a file called T.java
package test;
class T1 {}
class T2 {}
when i try to compile it it says cannot find symbol new T1(). When I put T1 in a separate file T1.java then it compiles fine. Why java is unable to find package private class in the same package.
javac will automatically compile all the linked file used in the file you are compiling if there .class files are not found. Like in your case ABC.java. But one thing to notice is javac will not search for all the files with .java extension to be compiled. But it will look for the file name with the same name as the class. Like in your case T1.
So if you will compile T.java and then compile ABC.java it will run as expected. But if you compile ABC.java and not T.java compiler will not find T1.class then it will look for T1.java, but it will not found it too, which will give you an error. On the other hand if you will rename T.java to T1.java it will work as expected.
In Java, When a class file name(T1.java) is same as class's name(T1) without public keyword, this class is public under this package(test)'s class.
I'm having a strange error. I have 2 classes in the same package but they can't find each other. From what I remember, as long as the classes are in the same package, they should be able to call each other's methods.
My code looks similar to this:
in A.java:
package com.mypackage;
public class A{
public static int read(){
//some code
}
}
in B.java:
package com.mypackage;
public class B{
public static void main(String args[]){
int x = A.read();
}
}
and it's giving me a cannot find symbol variable A error.
Both of these classes depend on some .jar files, but I've already included the path of those jars to CLASSPATH and A.java compiled fine, but B can't find A for some reasons...
When I remove the package com.mypackage; in both classes then they compile fine.
Since you're compiling Java files that are in distinct packages, you'll have to ensure that they compile to the appropriate directories.
You can use this invocation to do just that. Substitute $SRC with the location of your source files, and you can let $BIN be the current directory, or some other location on your machine.
javac -sourcepath $SRC -d $BIN A.java B.java
When you want to run them, you have to add them manually to the classpath again (but that's not such a bad thing).
java -cp $BIN com.mypackage.B
This invocation should work; just made sure of it with A.java and B.java residing on my desktop. With the -d flag, that ensured that when they compiled, they went to the appropriate package folder scheme.
It should be:
A.java
package com.mypackage;
class A {
public static int read(){
//some code
}
}
B.java
package com.mypackage;
class B {
public static void main(String args[]){
int x = A.read();
}
}
i have two programs
one in directory /home/redhat/Documents/java1/j1
Demo1.java
package j1;
public class Demo1
{
public void print()
{
System.out.println("hi");
}
}
and the other in directory /home/redhat/Documents/java1/j
Demo2.java
import j1.*;
public class Demo2
{
Demo2()
{
Demo1 d=new Demo1();
}
}
when i say
javac -classpath /home/redhat/Documents/java1/j1 Demo2.java
i get the following error
Demo2.java:2: package j1 does not exist
import j1.*;
^
Demo2.java:7: cannot access Demo1
bad class file: /home/redhat/Documents/java1/j1/Demo1.java
file does not contain class Demo1
Please remove or make sure it appears in the correct subdirectory of the classpath.
Demo1 d=new Demo1();
^
2 errors
i want to access instance of Demo1 in Demo2
please help.
Your classpath is wrong. You should point to the root of any declared packages:
javac -classpath /home/redhat/Documents/java1 Demo2.java
Other previous step that I miss is the compilation of Demo1 class. Javac compiler will look for ".class" files, not ".java" ones. So before executing that you need:
javac Demo1.java
As an improvement I would suggest you that you declare your second class inside package "j" instead of default package, since it is not a good idea to have root source paths inside another root path that already contains packages.
The classpath option specified in the command line of the javac executable is used to define the user classpath location where the compiler may find the compiled class files of types. In other words, the compiler expects compiled .class files in the user classpath.
In your case, you have a source class file, in which case you should use the sourcepath option of javac:
javac -sourcepath /home/redhat/Documents/java1 Demo2.java
javac will locate the j1 package under the user class path and hence resolve the type.