Question

我在驱动程序类的内部方法中有此代码（相关代码段）：

switch (op) {
    case "+":
        arithStack.push(new AddExpression(leftExpression, rightExpression));
        // System.out.println(arithStack.peek() + " :top of Stack");
        break;
    case "-":
        arithStack.push(new SubExpression(leftExpression, rightExpression));
        break;
    case "*":
        arithStack.push(new MultExpression(leftExpression, rightExpression));
        break;
    case "/":
        arithStack.push(new DivExpression(leftExpression, rightExpression));
        break;
    case "^":
        arithStack.push(new PowExpression(leftExpression, rightExpression));
        break;
    }

子类（AddExpression，SubExpressino等）是称为ArithBinaryExpression的抽象基类的子类。子类之一的实现如下所示（除算术运算外，与其他子类相同）：

    public static class AddExpression extends ArithBinaryExpression {
    public AddExpression(ArithExpression leftExp, ArithExpression rightExp) {
        super(leftExp, rightExp);
    }

    public double result() {
        ArithExpression rightExp = getRightExpression();
        ArithExpression leftExp = getLeftExpression();
        return rightExp.result() + leftExp.result();
    }

    public String toString() {
        return "Expression: " + "(" + leftExpression.toString() + " + " + rightExpression.toString() + ")";
    }

}

在这些子类构造函数的主要调用中，编译器给我一个错误：

arithStack.push(new AddExpression(leftExpression, rightExpression));

在这里编译器状态：

AddExpression无法解析为类型。我该如何解决？

更新：

（HERE是ArithBinaryExpression类）

public abstract class ArithBinaryExpression implements ArithExpression {
protected static ArithExpression leftExpression;
protected static ArithExpression rightExpression;

public boolean isSimple() {
    boolean isSimple = false;
    if (leftExpression instanceof ArithValue && rightExpression instanceof ArithValue) {
        isSimple = true;
    }
    return isSimple;
}
// constructor
public ArithBinaryExpression(ArithExpression left, ArithExpression right) {
    if (left == null) {
        leftExpression = new ArithValue(0);
    }
    else 
    leftExpression = left;

    if (right == null) {
        rightExpression = new ArithValue(0);
    }
    else
    rightExpression = right;


}
// end constructor

// accessors
public ArithExpression getLeftExpression() {
    return leftExpression;
}

public ArithExpression getRightExpression() {
    return rightExpression;
}

Answer 1

从类定义中删除static：

public class AddExpression extends ArithBinaryExpression {
    public AddExpression(ArithExpression leftExp, ArithExpression rightExp) {
        super(leftExp, rightExp);
    }

    public double result() {
        ArithExpression rightExp = getRightExpression();
        ArithExpression leftExp = getLeftExpression();
        return rightExp.result() + leftExp.result();
    }

    public String toString() {
        return "Expression: " + "(" + leftExpression.toString() + " + " + 
                rightExpression.toString() + ")";
    }

    public static void main(String args[]) {
       // create it here using new AddExpression ...
    }
}

Java不允许您创建顶级静态类。在Java中，如果new是static，则不能使用public class AddExpression创建新对象。

public static void main(String args[]) { // create it here using new AddExpression ... }必须是文件 addexpression.java 中唯一的公共类，并且必须正确导入或定义所有其他类。

要查看它是否正确创建，请使用您的

None

如何使驱动程序类中的方法看到另一个类的子类？

1 个答案: