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// Copyright 2014 Google Inc. All rights reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package com.google.devtools.build.buildjar.javac;
import com.sun.tools.javac.main.Main.Result;
import java.io.PrintWriter;
/**
* The JavacRunner is a type that can be used to invoke
* javac and provides a convenient hook for modifications.
* It is split in two parts: An interface "JavacRunner" and
* an implementation of that interface, "JavacRunnerImpl".
*
* The type is split in two parts to allow us to load
* the implementation multiple times in different classloaders.
* This is neccessary, as a single javac can not run multiple
* times in parallel. By using different classloaders to load
* different copies of javac in different JavacRunnerImpls,
* we can run them in parallel.
*
* However, since each JavacRunnerImpl will then be loaded
* in a different classloader, we then would not be able to
* refer to it by simply declaring a type as "JavacRunnerImpl",
* as this refers to the JavacRunnerImpl type loaded with the
* default classloader. Therefore, we'd have to address each
* of the different JavacRunnerImpls as "Object" and invoke
* its method via reflection.
*
* We can circumvent this problem by declaring an interface
* that JavacRunnerImpl implements (i.e. JavacRunner).
* If we always load this super-interface in the default
* classloader, and make each JavacRunnerImpl (loaded in its
* own classloader) implement it, we can refer to the
* JavacRunnerImpls as "JavacRunner"s in the main program.
* That way, we can avoid using reflection and "Object"
* to deal with the different JavacRunnerImpls.
*/
public interface JavacRunner {
Result invokeJavac(String[] args, PrintWriter output);
}
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