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samples/visitor/11-cleanversion/src-api3.0/org/apidesign/visitor/Language.java
author Jaroslav Tulach <jtulach@netbeans.org>
Sat, 14 Jun 2008 09:58:54 +0200
changeset 170 206cdfeefeec
child 171 2496512220b7
permissions -rw-r--r--
It always surprises me how things change when one really tries to implemente them. The whole approach with non-monotinic evolution was uncompilable. We need a common super type for all the visitors\! 
     1 package org.apidesign.visitor;

     2 

     3 public final class Language {

     4     private Language() { }

     5     

     6     public static abstract class Expression {

     7         public abstract void visit(Visitor v);

     8     }

     9     public static final class Plus extends Expression {

    10         private final Expression first;

    11         private final Expression second;

    12         

    13         public Plus(Expression first, Expression second) {

    14             this.first = first;

    15             this.second = second;

    16         }

    17         public Expression getFirst() { return first; }

    18         public Expression getSecond() { return second; }

    19         @Override

    20         public void visit(Visitor v) { v.visitPlus(this); }

    21     }

    22     public static final class Number extends Expression {

    23         private final int value;

    24         public Number(int value) { this.value = value; }

    25         public int getValue() { return value; }

    26         @Override

    27         public void visit(Visitor v) { v.visitNumber(this); }

    28     }

    29     /** @since 2.0 */

    30     public static final class Minus extends Expression {

    31         private final Expression first;

    32         private final Expression second;

    33         

    34         public Minus(Expression first, Expression second) {

    35             this.first = first;

    36             this.second = second;

    37         }

    38         public Expression getFirst() { return first; }

    39         public Expression getSecond() { return second; }

    40         

    41         public void visit(Visitor v) { 

    42             if (v instanceof Visitor2_0) {

    43                 ((Visitor2_0)v).visitMinus(this);

    44             } else {

    45                 v.visitUnknown(this);

    46             }

    47         }

    48     }

    49     // BEGIN: visitor.nonmonotonic.real

    50     /** @since 3.0 */

    51     public final class Real extends Expression {

    52         private final double value;

    53         public Real(double value) {

    54             this.value = value;

    55         }

    56         public double getValue() {

    57             return value;

    58         }

    59         public void visit(Visitor v)

    60         // FINISH: visitor.nonmonotonic.real

    61         {

    62         }

    63     }

    64 

    65     

    66     public interface Visitor {

    67         public void visitUnknown(Expression e);

    68     }

    69     public interface Visitor1_0 extends Visitor {

    70         public void visitPlus(Plus s);

    71         public void visitNumber(Number n);

    72     }

    73     /** @since 2.0 */

    74     public interface Visitor2_0 extends Visitor {

    75         public void visitMinus(Minus s);

    76     }

    77     // BEGIN: visitor.nonmonotonic.visitor

    78     /** @since 3.0 */

    79     public interface Visitor3_0 extends Visitor {

    80         public void visitPlus(Plus s);

    81         public void visitMinus(Minus s);

    82         public void visitReal(Number n);

    83     }

    84     // END: visitor.nonmonotonic.visitor

    85 }
hg/apidesign