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package composite.three;
public class ExprFactory2 {
private ExprFactory2() {}
static public Expr newConst(int v) {
return new Const(v);
}
static public Expr newPlus(Expr l, Expr r) {
return new PlusOp(l, r);
}
// static public Expr newMinus(Expr l, Expr r) {
// return new BinOp(l, new OpSub(), r);
// }
// static public Expr newMult(Expr l, Expr r) {
// return new BinOp(l, new OpMul(), r);
// }
// static public Expr newQuot(Expr l, Expr r) {
// return new BinOp(l, new OpDiv(), r);
// }
private static final class Const implements Expr {
private final int v;
public Const(int v) {
this.v = v;
}
public int eval() {
return v;
}
public String toString() {
return Integer.toString(v);
}
}
private static abstract class BinOp implements Expr {
private final Expr l;
private final Expr r;
private final String opString;
public BinOp(Expr l, String opString, Expr r) {
if ((l == null) || (r == null)) {
throw new IllegalArgumentException();
}
this.l = l;
this.r = r;
this.opString = opString;
}
protected abstract int run (int x, int y);
// to be template method, there must a template method
// template method = method of abstract class, that calls an abstract method
public int eval() {
return this.run(l.eval(), r.eval());
}
public String toString() {
return l.toString() + " " + r.toString() + " " + opString;
}
}
private static final class PlusOp extends BinOp {
public PlusOp(Expr l, Expr r) { super (l, "+", r); }
public int run(int x, int y) { return x+y; }
}
}
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