parametricexception.java

是一款用JAVA 编写的编译器 具有很强的编译功能

/*
 * Copyright 2002 Sun Microsystems, Inc.  All Rights Reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 */

/*
 * @test
 * @bug 4509267
 * @summary generics: parametric exception type versus overriding
 * @author gafter
 *
 * @compile -source 1.5 ParametricException.java
 */

import java.io.*; 

abstract class AChurchBoolean { 
    public abstract <Return, Parameter, Throws extends Throwable> 
    Return accept(IVisitor<Return, Parameter, Throws> visitor, Parameter parameter) throws Throws; 
    
    public interface IVisitor<Return, Parameter, Throws extends Throwable> { 
	public Return caseTrue(Parameter parameter) throws Throws; 
	public Return caseFalse(Parameter parameter) throws Throws; 
    } 
} 

class TrueChurchBoolean extends AChurchBoolean { 
    private static TrueChurchBoolean instance = new TrueChurchBoolean(); 
    private TrueChurchBoolean() {} 
    public static TrueChurchBoolean singleton() { 
	return instance; 
    } 
    public <Return, Parameter, Throws extends Throwable> 
    Return accept(IVisitor<Return, Parameter, Throws> visitor, Parameter parameter) throws Throws { 
	return visitor.caseTrue(parameter); 
    } 
} 

class FalseChurchBoolean extends AChurchBoolean { 
    private static FalseChurchBoolean instance = new FalseChurchBoolean(); 
    private FalseChurchBoolean() {} 
    public static FalseChurchBoolean singleton() { 
	return instance; 
    } 
    public <Return, Parameter, Throws extends Throwable> 
    Return accept(IVisitor<Return, Parameter, Throws> visitor, Parameter parameter) throws Throws { 
	return visitor.caseFalse(parameter); 
    } 
} 

class Pair<T,U> { 
    private T first; 
    private U second; 
    Pair(T first, U second) { 
	this.first = first; 
	this.second = second; 
    } 
    T getFirst() { 
	return first; 
    } 
    U getSecond() { 
	return second; 
    } 
} 

// Perhaps a bit of a toy example, but relevant nonetheless. 
class ChurchBooleanTest { 
    private AChurchBoolean bool; 
    public ChurchBooleanTest(AChurchBoolean bool) { 
	this.bool = bool; 
    } 
    public AChurchBoolean readIf(File file, byte[] output) throws IOException { 
	return bool.accept(new AChurchBoolean.IVisitor<AChurchBoolean, Pair<File, byte[]>, IOException>() { 
	    public AChurchBoolean caseTrue(Pair<File, byte[]> parameter) throws IOException { 
		FileInputStream input = new FileInputStream(parameter.getFirst()); // throws 
		input.read(parameter.getSecond()); // throws 
		input.close(); // throws 
		return TrueChurchBoolean.singleton(); 
	    } 
	    public AChurchBoolean caseFalse(Pair<File, byte[]> parameter) throws IOException { 
		return FalseChurchBoolean.singleton(); 
	    } 
	}, new Pair<File, byte[]>(file, output)); 
    } 
}