numbervalue.java

是有关解释器的.用JAVA编写.可以解释一般的JAVA程序.

public class NumberValue extends Value {
    private int value;

    NumberValue() {
        value = 0;
    }

    NumberValue(int i) {
        value = i;
    }

    boolean isNumber() {
        return true;
    }

    int numberValue() {
        return value;
    }

    boolean isOfType(String typeName) {
        return typeName.equals("int");
    }

    public String toString() {
        return "" + value;
    }

    Value plus(Value v) throws InterpreterException {
        if (!v.isNumber())
            throw new InterpreterException(
                    "This type does not support addition.");

        return new NumberValue(value + ((NumberValue) v).numberValue());
    }

    Value minus(Value v) throws InterpreterException {
        if (!v.isNumber())
            throw new InterpreterException(
                    "This type does not support substraction.");

        return new NumberValue(value - ((NumberValue) v).numberValue());
    }

    Value multipliedBy(Value v) throws InterpreterException {
        if (!v.isNumber())
            throw new InterpreterException(
                    "This type does not support multiplication.");

        return new NumberValue(value * ((NumberValue) v).numberValue());
    }

    Value dividedBy(Value v) throws InterpreterException {
        if (!v.isNumber())
            throw new InterpreterException(
                    "This type does not support division.");

        if (((NumberValue) v).value == 0)
            throw new InterpreterException("Division by zero.");

        return new NumberValue(value / ((NumberValue) v).numberValue());
    }

    Value isLess(Value v) throws InterpreterException {
        if (!v.isNumber())
            throw new InterpreterException(
                    "This type does not support less comparison.");

        return new BooleanValue(value < ((NumberValue) v).numberValue());
    }

    Value isGreater(Value v) throws InterpreterException {
        if (!v.isNumber())
            throw new InterpreterException(
                    "This type does not support greater comparison.");

        return new BooleanValue(value > ((NumberValue) v).numberValue());
    }

    Value isEqual(Value v) throws InterpreterException {
        if (!v.isNumber())
            throw new InterpreterException(
                    "This type does not support equation.");

        return new BooleanValue(value == ((NumberValue) v).numberValue());
    }

    Value negate() throws InterpreterException {
        return new NumberValue(-value);
    }

    Value assign(Value v) throws InterpreterException {
        if (!v.isNumber())
            throw new InterpreterException("wrong type.");

        this.value = ((NumberValue) v).numberValue();
        return this;
    }

    Value cloneValue() {
        return new NumberValue(value);
    }
}