package java.nio.file does not exist

Question

I'm working out how to compile java from command line at the moment. Here's what I've got:

Here's what I've got:

/myjava/compile.cmd
/myjava/src/a_pack/HelloWorld.java
/myjava/src/b_pack/Inner.java
/myjava/src/b_pack/Inner2.java
/myjava/bin

HelloWorld:

package a_pack;

import b_pack.Inner;
import b_back.Inner2;
import java.util.ArrayList; 
import java.util.Iterator; 

public class HelloWorld {

    public static void main(String[] args) {

        System.out.println("Hello, World");     

        Inner myInner = new Inner(); 
        myInner.myInner(); 

        Inner2 myInner2 = new Inner2();
        myInner2.myInner(); 


        ArrayList myArray = new ArrayList(); 
        myArray.add(1); 
        myArray.add(2); 
        myArray.add(3); 

        Iterator itr = myArray.iterator();
        while (itr.hasNext())
        {
            System.out.println(itr.next()); 
        }

    }

}

Inner.java

package b_pack; 

public class Inner {

    public void myInner() {
        System.out.println("Inner Method");
    }

}

Inner2.java

package b_pack; 

public class Inner2 {

    public void myInner() {
        System.out.println("SecondInner");
    }

}

I'm compiling this with javac -d bin -sourcepath -src src/a_pack/HelloWorld.java and this works fine.

Now my understanding is, that because the HelloWorld.java references the other packages in it's import statements, then javac goes and compiles those. And I'm guessing that for all the java packages, javac has them internally or something.

Anyway - if I add the following import line to HelloWorld.java

import java.nio.file.Files;

it fails with

D:\.....\myjava>javac -d bin -sourcepath src src/a_pack/HelloWo
rld.java
src\a_pack\HelloWorld.java:8: package java.nio.file does not exist
import java.nio.file.Files;
                    ^
1 error

What's the story here? Why are some java packages good and some not?

Answer 1

Java NIO was introduced in Java 7. Compilers from earlier versions of the JDK will baulk at any code that contains these NIO classes. You need to upgrade to JDK 7 or higher.

Answer 2

If you are on OSX, then check the JDK it is using...

$ cd /System/Library/Frameworks/JavaVM.framework/Versions
$ readlink /System/Library/Frameworks/JavaVM.framework/Versions/CurrentJDK
/System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents
$ javac -version
javac 1.7.0_25

As you can see CurrentJDK is pointing to the wrong version. You can fix that by replacing the symlink.

cd /System/Library/Frameworks/JavaVM.framework/Versions
sudo ln -fs /Library/Java/JavaVirtualMachines/jdk1.7.0_25.jdk/Contents CurrentJDK

Credit goes to this blog post which saved me 5min of running dtrace.

Answer 3

I came across this issue and found my JAVA_HOME environment variable was still pointing to the old java 1.6.

• Running javac -version showed 1.7
• Running java -version showed 1.7

etc…

On removing that environment variable, things compiled fine.

Answer 4

The Files class consists of only static methods. I'm not sure if this is why it can't be imported, but it does mean it doesn't need to be imported.

Edit: Just realized the package you specified is import java.nio.files.Files. The actual package is java.nio.file.Files; http://docs.oracle.com/javase/7/docs/api/java/nio/file/package-summary.html