学步园

行为模式涉及到算法和对象间职责的分配。
interpreter:给定一个语言，定义它的文法的一种表示，并定义一个解释器，这个解释器用来解释语言中的句子。

package behaviour.interpreter;

import behaviour.interpreter.mypackage.BooleanExp;

/**
 *  A NonterminalExpression
 */
public class AndExp implements BooleanExp {
    private BooleanExp operand1;
    private BooleanExp operand2;
   
    public AndExp(BooleanExp oper1, BooleanExp oper2) {
        operand1 = oper1;
        operand2 = oper2;
    }

    public boolean Evaluate(Context c) {
        return operand1.Evaluate(c) &&
                    operand2.Evaluate(c);
    }

    public BooleanExp Copy() {
        return new AndExp(operand1.Copy(), operand2.Copy());
    }

    public BooleanExp Replace(String var, BooleanExp exp) {
        return new AndExp(
                    operand1.Replace(var, exp),
                    operand2.Replace(var, exp)
                    );
    }
}

package behaviour.interpreter;
/**
 *  A Context to record variable value
 */
import java.util.*;

public class Context  {
    private Hashtable context = new Hashtable();
    public void Assign(String name, boolean val) {
        context.put(name, new Boolean(val));
    }
    public boolean LookUp(String name) {
        return ((Boolean)context.get(name)).booleanValue();
    }
    public Context() {
    }
}

package behaviour.interpreter;

import behaviour.interpreter.mypackage.BooleanExp;

/**
 *  A NonterminalExpression
 */
public class NotExp implements BooleanExp {
    private BooleanExp opernot1;
    //private BooleanExp operor2;
   
    public NotExp(BooleanExp oper1) {
        opernot1 = oper1;
    }

    public boolean Evaluate(Context c) {
        return !(opernot1.Evaluate(c));
    }

    public BooleanExp Copy() {
        return new NotExp(opernot1.Copy());
    }

    public BooleanExp Replace(String var, BooleanExp exp) {
        return new NotExp(opernot1.Replace(var, exp));
    }
}

package behaviour.interpreter;

import behaviour.interpreter.mypackage.BooleanExp;

/**
 *  A NonterminalExpression
 */
public class OrExp implements BooleanExp {
    private BooleanExp operor1;
    private BooleanExp operor2;
   
    public OrExp(BooleanExp oper1, BooleanExp oper2) {
        operor1 = oper1;
        operor2 = oper2;
    }

    public boolean Evaluate(Context c) {
        return operor1.Evaluate(c) ||
                    operor2.Evaluate(c);
    }

    public BooleanExp Copy() {
        return new OrExp(operor1.Copy(), operor2.Copy());
    }

    public BooleanExp Replace(String var, BooleanExp exp) {
        return new OrExp(
                    operor1.Replace(var, exp),
                    operor2.Replace(var, exp)
                    );
    }
}

package behaviour.interpreter;
/**
 *
 */
import java.io.*;
import java.util.*;

import behaviour.interpreter.mypackage.BooleanExp;

public class Test  {
    public static void main(String[] args) {
        // Test :
        //         (true and x) and (y and (not x))
        Context context = new Context();
      
        VariableExp x = new VariableExp("X");
        VariableExp y = new VariableExp("Y");
        VariableExp bTure = new VariableExp("true");
        VariableExp bFalse = new VariableExp("false");

        context.Assign("true", true);
        context.Assign("false", false);
        context.Assign("X", false);
        context.Assign("Y", true);
       
        BooleanExp expression = new AndExp(
            new AndExp(bTure, x),
            new AndExp(y, new NotExp(x))
        );
        boolean result = expression.Evaluate(context);
        System.out.println("The result is:" + result);
    }
}

package behaviour.interpreter;
/**
 *  A variable expression implements BooleanExp
 *  A terminal expression
 */
import java.util.*;

import behaviour.interpreter.mypackage.BooleanExp;

public class VariableExp implements BooleanExp {
    private String name;
   
    public VariableExp(String _name) {
        name = _name;
    }

    public boolean Evaluate(Context c) {
        return c.LookUp(name);
    }

    public BooleanExp Copy() {
        return new VariableExp(name);
    }

    public BooleanExp Replace(String var, BooleanExp exp) {
        if(var.equals(name)) {
            return exp.Copy();
        } else {
            return new VariableExp(name);
        }
    }
   
}

package behaviour.interpreter.mypackage;

import behaviour.interpreter.Context;

/**
 *  The interface of our BooleanExp Interpreter
 *  BooleanExp definition is:
 *      BooleanExp ::= VariableExp | Constant | OrExp | AndExp
 *                               | NotExp | '(' BooleanExp ')'
 *      AndExp ::= BooleanExp 'and' BooleanExp
 *      OrExp ::= BooleanExp 'or' BooleanExp
 *      NotExp ::= BooleanExp 'not' BooleanExp
 *      Constant ::= 'true' | 'false'
 *      VariableExp ::= 'A' | 'B' | ... | 'Z'
 */

public interface BooleanExp {
    public abstract boolean Evaluate(Context c);
    public abstract BooleanExp Replace(String var, BooleanExp exp);
    public abstract BooleanExp Copy();
}