java方法中的逻辑问题

Question

当我尝试运行此代码时，它不断返回错误的值，并且我无法弄清楚哪里出了问题。在我将 10 添加到 catUp 后，它会正确打印出来，但是当我检查相同的值是否大于 199 时，由于某种原因，它会通过该 if 语句。另外，当我在 upCategory 方法末尾打印它时，它给出的值是 1，但是当我在 main 中打印它时，它给出的值是 3。

 public void upCategory()
  {
    double catUp = radioXM.getCurrentStaion();
    catUp += 10;
    System.out.println(catUp);
    if (catUp > 199.0);
    {
      catUp = 1; 
      radioXM.setCurrentStation(catUp);
      System.out.println(catUp);
    }
    radioXM.setCurrentStation(catUp);
    System.out.println(catUp);
  }
 public static void main (String [] args) { 
    AutoRadioSystem c = new AutoRadioSystem();
    c.selectRadio();
    double b = c.getCurrentStation();
    System.out.println(b);

    // this changes the radio to XM
    c.selectRadio();
    double d = c.getCurrentStation();
    System.out.println(d);

    //this is suppose to change the station up by 10 but gives incorrect value
    c.upCategory();
    double f = c.getCurrentStation();
    System.out.println(f);
  }

附带的附加代码...

public abstract class Radio 
{
 double currentStation;

 RadioSelectionBar radioSelectionBar;
 public Radio()
 {
   this.currentStation = getMin_Station();
 }
 public abstract double getMax_Station();
 public abstract double getMin_Station();
 public abstract double getIncrement();
 public void up()
 {

 }
 public void down()
 {

 }
 public double getCurrentStaion()
 {
   return this.currentStation;
 }
 public void setCurrentStation(double freq)
 {
   currentStation += freq;
 }
 public void setStation(int buttonNumber, double station)
 {
 }
 public double getStation(int buttonNumber)
 {
   return 0.0;
 }
 public String toString()
 {
   String message = ("" + currentStation);
   return message;
 } 
  public boolean equals (Object o) 
  {
    if (o == null) 
      return false; 
    if (! (o instanceof Radio)) 
      return false; 
    Radio other = (Radio) o; 
    return this.currentStation == other.currentStation;
  }

public class XMRadio extends Radio
{
  private static final double Max_Station = 199;
  private static final double Min_Station = 1;
  private static final double Increment = 1;
  public XMRadio()
  {
  }
  public double getMax_Station()
  {
    return this.Max_Station;
  }
  public  double getMin_Station()
  {
    return this.Min_Station;
  }
  public  double getIncrement()
  {
    return this.Increment;
  }
  public String toString()
  {
    String message = ("XM "+ currentStation );
    return message;
  } 
}

Answer 1

这一行是问题所在:

if (catUp > 199.0);

Java将分号视为if语句的主体，if下面的大括号中的 block 成为普通 block ，并且始终被执行。

要将大括号中的 block 附加到 if 语句，请删除分号:

if (catUp > 199.0)