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3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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8  *
9  * This code is distributed in the hope that it will be useful, but WITHOUT
10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
12  * version 2 for more details (a copy is included in the LICENSE file that
13  * accompanied this code).
14  *
15  * You should have received a copy of the GNU General Public License version
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17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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23 
24 /*
25  * @test
26  * @bug 4509267
27  * @summary generics: parametric exception type versus overriding
28  * @author gafter
29  *
30  * @compile  ParametricException.java
31  */
32 
33 import java.io.*;
34 
35 abstract class AChurchBoolean {
36     public abstract <Return, Parameter, Throws extends Throwable>
accept(IVisitor<Return, Parameter, Throws> visitor, Parameter parameter)37     Return accept(IVisitor<Return, Parameter, Throws> visitor, Parameter parameter) throws Throws;
38 
39     public interface IVisitor<Return, Parameter, Throws extends Throwable> {
caseTrue(Parameter parameter)40         public Return caseTrue(Parameter parameter) throws Throws;
caseFalse(Parameter parameter)41         public Return caseFalse(Parameter parameter) throws Throws;
42     }
43 }
44 
45 class TrueChurchBoolean extends AChurchBoolean {
46     private static TrueChurchBoolean instance = new TrueChurchBoolean();
TrueChurchBoolean()47     private TrueChurchBoolean() {}
singleton()48     public static TrueChurchBoolean singleton() {
49         return instance;
50     }
51     public <Return, Parameter, Throws extends Throwable>
accept(IVisitor<Return, Parameter, Throws> visitor, Parameter parameter)52     Return accept(IVisitor<Return, Parameter, Throws> visitor, Parameter parameter) throws Throws {
53         return visitor.caseTrue(parameter);
54     }
55 }
56 
57 class FalseChurchBoolean extends AChurchBoolean {
58     private static FalseChurchBoolean instance = new FalseChurchBoolean();
FalseChurchBoolean()59     private FalseChurchBoolean() {}
singleton()60     public static FalseChurchBoolean singleton() {
61         return instance;
62     }
63     public <Return, Parameter, Throws extends Throwable>
accept(IVisitor<Return, Parameter, Throws> visitor, Parameter parameter)64     Return accept(IVisitor<Return, Parameter, Throws> visitor, Parameter parameter) throws Throws {
65         return visitor.caseFalse(parameter);
66     }
67 }
68 
69 class Pair<T,U> {
70     private T first;
71     private U second;
Pair(T first, U second)72     Pair(T first, U second) {
73         this.first = first;
74         this.second = second;
75     }
getFirst()76     T getFirst() {
77         return first;
78     }
getSecond()79     U getSecond() {
80         return second;
81     }
82 }
83 
84 // Perhaps a bit of a toy example, but relevant nonetheless.
85 class ChurchBooleanTest {
86     private AChurchBoolean bool;
ChurchBooleanTest(AChurchBoolean bool)87     public ChurchBooleanTest(AChurchBoolean bool) {
88         this.bool = bool;
89     }
readIf(File file, byte[] output)90     public AChurchBoolean readIf(File file, byte[] output) throws IOException {
91         return bool.accept(new AChurchBoolean.IVisitor<AChurchBoolean, Pair<File, byte[]>, IOException>() {
92             public AChurchBoolean caseTrue(Pair<File, byte[]> parameter) throws IOException {
93                 FileInputStream input = new FileInputStream(parameter.getFirst()); // throws
94                 input.read(parameter.getSecond()); // throws
95                 input.close(); // throws
96                 return TrueChurchBoolean.singleton();
97             }
98             public AChurchBoolean caseFalse(Pair<File, byte[]> parameter) throws IOException {
99                 return FalseChurchBoolean.singleton();
100             }
101         }, new Pair<File, byte[]>(file, output));
102     }
103 }
104