Výrazy - Composite, Interpreter, Visitor

Představuje libovolný výraz

package vyrazy;
 
import java.io.IOException;
 
abstract public class Expr {
    abstract double eval();
    @Override
    public abstract String toString();
    public abstract void exportUsing(Exporter exporter) throws IOException;
}

Představuje konstantní hodnotu

package vyrazy;
 
import java.io.IOException;
public class Value extends Expr{
    double x;
    public Value(double x){
        this.x = x;
    }
 
    @Override
    double eval() {
        return x;
    }
 
    @Override
    public String toString() {
        return String.valueOf(x);
    }
 
    @Override
    public void exportUsing(Exporter exporter) throws IOException {
        exporter.exportValue(this);
    }
}

Společná nadtřída binárních operací

package vyrazy;
 
abstract public class BinOp extends Expr{
    Expr op1;
    Expr op2;
 
    public BinOp(Expr x, Expr y){
        op1 = x;
        op2 = y;
    }
}

package vyrazy;
 
import java.io.IOException;
 
public class Plus extends BinOp{
 
    public Plus(Expr x, Expr y){
        super(x,y);
    }
 
    @Override
    double eval() {
        return op1.eval() + op2.eval();
    }
 
    @Override
    public String toString() {
        return op1.toString() + " + " + op2.toString();
    }
 
    @Override
    public void exportUsing(Exporter exporter) throws IOException {
        exporter.exportPlus(this);
    }
}

package vyrazy;
 
import java.io.IOException;
 
public class Multiply extends BinOp{
 
    public Multiply(Expr x, Expr y){
        super(x,y);
    }
 
    @Override
    double eval() {
        return op1.eval() * op2.eval();
    }
 
    @Override
    public String toString() {
        return op1.toString() + " * " + op2.toString();
    }
 
    @Override
    public void exportUsing(Exporter exporter) throws IOException {
        exporter.exportMultiply(this);
    }
}

Definuje společný kód a rozhraní exportéru do textového souboru.

package vyrazy;
 
import java.io.IOException;
import java.io.Writer;
 
public abstract class Exporter {
    Writer writer;
 
    public Exporter(Writer writer) {
        this.writer = writer;
    }
 
    abstract void exportValue(Value expr) throws IOException;
    abstract void exportPlus(Plus expr) throws IOException;
    abstract void exportMultiply(Multiply expr) throws IOException;
 
    void exportExpr(Expr expr) throws IOException {
        expr.exportUsing(this);
    }
 
}

Konkrétní implementace exportéru, v infixové notaci.

package vyrazy;
 
import java.io.IOException;
import java.io.Writer;
 
public class TextExporter extends Exporter {
    public TextExporter(Writer writer) {
        super(writer);
    }
 
    void exportValue(Value expr) throws IOException {
        writer.write(String.valueOf(expr.x));
    }
 
    @Override
    void exportPlus(Plus expr) throws IOException {
        expr.op1.exportUsing(this);
        writer.write(" + ");
        expr.op2.exportUsing(this);
    }
 
    void exportMultiply(Multiply expr) throws IOException {
        expr.op1.exportUsing(this);
        writer.write(" * ");
        expr.op2.exportUsing(this);
    }
 
}

Exportér v postfixové notaci.

package vyrazy;
 
import java.io.IOException;
import java.io.Writer;
 
public class PostfixTextExporter extends Exporter {
    public PostfixTextExporter(Writer writer) {
        super(writer);
    }
 
    void exportValue(Value expr) throws IOException {
        writer.write(String.valueOf(expr.x));
    }
 
    @Override
    void exportPlus(Plus expr) throws IOException {
        expr.op1.exportUsing(this);
        writer.write(" ");
        expr.op2.exportUsing(this);
        writer.write(" +");
    }
 
    @Override
    void exportMultiply(Multiply expr) throws IOException {
        expr.op1.exportUsing(this);
        writer.write(" ");
        expr.op2.exportUsing(this);
        writer.write(" *");
    }
}

package vyrazy;
 
import java.io.IOException;
import java.io.StringWriter;
import java.io.Writer;
 
public class Main {
 
    public static void main(String[] args) throws IOException {
        Expr vyraz = new Multiply (new Value(1), new Value(3));
        vyraz = new Plus (vyraz, new Value(4));
 
        /* soubor emulujeme StringWriterem */
        Writer w = new StringWriter();
 
        Exporter ex = new TextExporter(w);
        ex.exportExpr(vyraz);
 
        System.out.println(w);
    }
 
}