# Call the Java Compiler from Processing
**URL:** https://discourse.processing.org/t/call-the-java-compiler-from-processing/35076
**Category:** Coding Questions
**Created:** [February 10, 2022, 5:13pm UTC](https://discourse.processing.org/t/call-the-java-compiler-from-processing/35076 "2022-02-10T17:13:05Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@NumericPrime](https://discourse.processing.org/u/NumericPrime)
#### Post date: [February 10, 2022, 5:13pm UTC](https://discourse.processing.org/t/call-the-java-compiler-from-processing/35076/1 "2022-02-10T17:13:06Z")
I’m currently writing a library for a few friends of mine who use Processing and it would be cool if I were to include a possibiity to compile and run Java-code.
I used a code I already used for another project. However when trying to include it in Processing I run in a few problems. Here ist the code I used:
```auto
import java.io.File;
import java.nio.file.Files;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.PrintStream;
import java.io.PrintWriter;
import java.net.URL;
import java.net.URLClassLoader;
import java.nio.charset.StandardCharsets;
import javax.tools.JavaCompiler;
import javax.tools.ToolProvider;
void settings() {
File root = new File(sketchPath()+"/compiledPrograms");
println(root.getAbsolutePath());
try {
String source = "public class CompiledProgram{public static void main(String[] args){System.out.println(\"Hello World\"); }}";
// Save source in .java file. // On Windows running on C:\, this is C:\java.
File sourceFile = new File(root, "CompiledProgram.java");
sourceFile.getParentFile().mkdirs();
Files.write(sourceFile.toPath(), source.getBytes(StandardCharsets.UTF_8));
// Compile source file.
JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
Class cls = null ;
//Here the error happens
compiler.run(null, null, null, sourceFile.getPath());
URLClassLoader classLoader = URLClassLoader.newInstance(new URL[] { root.toURI().toURL() });
cls = Class.forName("CompiledProgram", true, classLoader);
Object instance=cls.newInstance();
}
catch(Exception e) {
e.printStackTrace();
}
}
```
Here is the stack-trace:
java.lang.NullPointerException
at CompilerTest.settings(CompilerTest.java:55)
at processing.core.PApplet.handleSettings(PApplet.java:973)
at processing.core.PApplet.runSketch(PApplet.java:10751)
at processing.core.PApplet.main(PApplet.java:10476)
How can I prevent this from happening?
Edit: I removed an error.
---
### Author:  [@th75](https://discourse.processing.org/u/th75)
#### Post date: [February 11, 2022, 12:22am UTC](https://discourse.processing.org/t/call-the-java-compiler-from-processing/35076/2 "2022-02-11T00:22:32Z")
hi NumericPrime,
just replace settings() by setup() and it will work
only few things can be done in settings as said [here](https://processing.org/reference/settings_.html)
otherwise it s interesting can you give a hint on when using this ‘inside’ compilation?
EDIT: oops i spoke too fast i think it doesn t do what you want, i had to replace settings to run it but still not doing more than writting the .java file
---
### Author:  [@quark](https://discourse.processing.org/u/quark)
#### Post date: [February 11, 2022, 11:51am UTC](https://discourse.processing.org/t/call-the-java-compiler-from-processing/35076/3 "2022-02-11T11:51:04Z")
> [@NumericPrime](#):
>
> `String source = "public class CompiledProgram(){public static void main(String[] args){System.out.println(\"Hello World\"); }}";`
There is an error in this line should be
`String source = "public class CompiledProgram{public static void main(String[] args){System.out.println(\"Hello World\"); }}";`
without the parenthesises after the class name.
The source must have correct Java syntax otherwise it will fail to compile.
---
### Author:  [@NumericPrime](https://discourse.processing.org/u/NumericPrime)
#### Post date: [February 11, 2022, 12:23pm UTC](https://discourse.processing.org/t/call-the-java-compiler-from-processing/35076/4 "2022-02-11T12:23:11Z")
Well that is embaressing… Thank you!
Update: It still doesn’t work. Same exception.
---
### Author:  [@quark](https://discourse.processing.org/u/quark)
#### Post date: [February 11, 2022, 3:30pm UTC](https://discourse.processing.org/t/call-the-java-compiler-from-processing/35076/5 "2022-02-11T15:30:08Z")
I tried the code below in both Processing and Eclipse. It worked fine in Eclipse but was unable to create the compiler in Processing. I have no idea why
```auto
import java.io.File;
import java.net.URL;
import java.net.URLClassLoader;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import javax.tools.JavaCompiler;
import javax.tools.ToolProvider;
public void settings() {
size(300, 300);
}
public void setup() {
File root = new File(sketchPath()+"/compiledPrograms");
println(root.getAbsolutePath());
try {
String source = "public class CompiledProgram{public static void main(String[] args){System.out.println(\"Hello World\"); }}";
// Save source in .java file. // On Windows running on C:\, this is C:\java.
File sourceFile = new File(root, "CompiledProgram.java");
sourceFile.getParentFile().mkdirs();
Files.write(sourceFile.toPath(), source.getBytes(StandardCharsets.UTF_8));
// Compile source file.
JavaCompiler compiler = (JavaCompiler) ToolProvider.getSystemJavaCompiler();
if (compiler == null)
println("No compiler");
//Here the error happens beacuase compiler == null
compiler.run(null, null, null, sourceFile.getPath());
URLClassLoader classLoader = URLClassLoader.newInstance(new URL[] { root.toURI().toURL() });
Class cls = null ;
cls = Class.forName("CompiledProgram", true, classLoader);
if (cls == null)
println("No class loader");
Object instance=cls.newInstance();
if (instance == null)
println("No instance created");
}
catch(Exception e) {
e.printStackTrace();
}
}
```