Illustrate the varcode Java API to Author, Compile, Use and Export Ad Hoc code at runtime

quickstart.APIInANutshell.java

package quickstart;

import java.io.Serializable;
import java.util.UUID;
import varcode.java.Java;
import varcode.java.adhoc.Export;
import varcode.java.meta._class;

/**
 *
 * Simple things should be simple, 
 * complex things should be possible --Alan Kay 
 */
public class APIInANutshell    
{
    public static void main( String[] args )
    {
        buildAuthorCompileUseAndExportAdHocCode();
        loadModifyCompileUseAndExportAdHocCode();
    }
    
    public static void buildAuthorCompileUseAndExportAdHocCode()
    {
        //model a class
        _class _adHoc = _class.of( "public class A" )
            .method( "public String toString()",
                "return \"Hello World\";" );
        
        //write the source ("A.java") to a file
        Export.dir("C:\\myprog\\src\\main\\java\\").file( _adHoc );
        
        //compile the "A.java" to "A.class", & create a new instance
        Object adHocA = _adHoc.instance( );
        
        //write "A.class" bytecode to a file 
        Export.dir("C:\\myprog\\target\\classes\\").file( adHocA.getClass() );
        
        //call a method on the adHoc instance (msg = "Hello World!")
        String msg = (String)Java.call( adHocA, "toString" );   
        
        System.out.println( msg );        
    }
    
    /**
     * This Class will have it's source code: 
     * <UL>
     *  <LI> read in at runtime 
     *  <LI> converted to an AST
     *  <LI> converted the AST into a _class (meta model)
     * </UL>
     */
    public class ExistingClass
        implements Serializable
    {
        //we are just putting a field her which will be modelled
        public String existing = "BLAH";
        
    }
    
    public static void loadModifyCompileUseAndExportAdHocCode()
    {
        // load the _class model of an existing class (even an inner class)
        _class _cload = Java._classFrom( ExistingClass.class );
        
        //change class name & package, add an import, field, & method
        _cload.setName( "Tailored" )
            .packageName( "ex.load.then.tailor" )
            .field( "public static final int ID = 100;" )
            .imports( UUID.class )
            .method( "public String toString()",
                "return existing + UUID.randomUUID().toString();" );
        
        //write the modified "ex.load.then.tailor.Tailored.java" source
        Export.TEMP_DIR.file( _cload );
        
        // compile & 
        Object tailored = _cload.instance(  );
        
        System.out.println( tailored );        
        
        //write "ex.load.then.tailor.Tailored.class" bytecode to a file
        Export.TEMP_DIR.file( tailored.getClass() );
    }
}

buildAuthorCompileUseAndExportAdHocCode(), exports the File:

public class A
{

    public String toString(  )
    {
        return "Hello World";
    }
}

loadModifyCompileUseAndExportAdHocCode(), exports the File:

package ex.load.then.tailor;

import java.io.Serializable;
import java.util.UUID;
import varcode.java.Java;
import varcode.java.adhoc.Export;
import varcode.java.meta._class;


/**
 *  This Class will have it's source code:
 *  <UL>
 *   <LI> read in at runtime
 *   <LI> converted to an AST
 *   <LI> converted the AST into a _class (meta model)
 *  </UL>
 */
public class Tailored
    implements Serializable
{
    public static final int ID = 100;
    public String existing = "BLAH";

    public String toString(  )
    {
        return existing + UUID.randomUUID().toString();
    }
}