Question

我是Java课程的初级学生，所以这对你们来说可能看起来很愚蠢。这是代码。

class CyclingResult implements IEvent {
  double time;
  int finishOrder;

  CyclingResult(double time, int finishOrder) {
    this.time = time;
    this.finishOrder = finishOrder;
  }

  public double pointsEarned() {
    return if (this.finishOrder == 1) {
      (this.time - 10);
    } else if (this.finishOrder == 2) {
      (this.time - 7);
    } else if (this.finishOrder == 3) {
      (this.time - 3);
    } else {
      this.time;
    }
  }
}

我得到一组5＆＃34;错误：语法错误，插入＆＃34; AssignmentOperator Expression＆＃34;完成表达＆＃34;

我确信我的代码有些愚蠢，但我能找到的例子有点超出我的想法来找出差异。

Answer 1

您无法在Java中返回if语句。与其他语言（例如Scala）不同，if语句就是：语句（没有值）。

您需要分别在每个if / else块内返回。

public double pointsEarned() {
    if (this.finishOrder == 1) {
      return (this.time - 10);
    } else if (this.finishOrder == 2) {
      return (this.time - 7);
    } else if (this.finishOrder == 3) {
      return (this.time - 3);
    } else {
      return this.time;
    }
  }

Answer 2

最接近你要做的是嵌套条件运算符：

return (this.finishOrder == 1) ? (this.time - 10)
     : (this.finishOrder == 2) ? (this.time - 7)
     : (this.finishOrder == 3) ? (this.time - 3)
     : this.time;

您无法使用return if ...，因为if is a statement，not an expression。

Answer 3

您未正确返回该值。如果要立即返回值，则必须对每个条件使用return。

public double pointsEarned() {
    if (this.finishOrder == 1) {
        return (this.time - 10);
    } else if (this.finishOrder == 2) {
        return (this.time - 7);
    } else if (this.finishOrder == 3) {
        return (this.time - 3);
    }
    return this.time;
}

对于多个if / else-if语句，您应该考虑使用switch语句：

public double pointsEarned() {
    switch (this.finishOrder) {
        case 1:
            return (this.time - 10);
        case 2:
            return (this.time - 7);
        case 3:
            return (this.time - 3);
        default:
            break;
    }
    return this.time;
}

如果Else AssignmentOperator问题 - Java

3 个答案: