====== Výrazy - Composite, Interpreter, Visitor ======

===== Expr.java =====
Představuje libovolný výraz

<code java>
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;
}
</code>


===== Value.java =====
Představuje konstantní hodnotu

<code java>
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);
    }
}
</code>


===== BinOp.java =====
Společná nadtřída binárních operací

<code java>
package vyrazy;

abstract public class BinOp extends Expr{
    Expr op1;
    Expr op2;

    public BinOp(Expr x, Expr y){
        op1 = x;
        op2 = y;
    }
}
</code>

===== Plus.java =====

<code java>
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);
    }
}
</code>

===== Multiply.java =====

<code java>
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);
    }
}
</code>

===== Exporter.java =====
Definuje společný kód a rozhraní exportéru do textového souboru.

<code java>
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);
    }

}
</code>


===== TextExporter.java =====
Konkrétní implementace exportéru, v infixové notaci.

<code java>
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);
    }

}
</code>


===== PostfixTextExporter.java =====
Exportér v postfixové notaci.

<code java>
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(" *");
    }
}
</code>

===== Main.java =====

<code java>
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);
    }

}
</code>