java为什么我的代码打印出0.00而不是45.000

Question

//Single parameter 
public Time(double input){
  number=  20.75;
  double temp ;

  temp=  (number%1*60*100)/100; // Prints out 0.00 why?
  minutes= (int)temp;
  hours= (int)number-(int)number%1;
}

我的代码运行得非常好，但我有点困惑，为什么它会为temp变量打印出0.00，而不是45.0000

我认为它是如何工作的：number=20.75，因此20.75万%1=0.75万*60*100/100=45.0000，因此temp=45.00000

以下是完整代码：

 public class TimetestProgram {
  public static void main(String[]args){
    Time object =  new Time(20,329);
    Time gamma= new Time(20.75);
    System.out.println(object);
    System.out.println(gamma);
    System.out.println("temp:"+gamma.temp);
    System.out.println("minutes:"+gamma.minutes);
    System.out.println("number:"+gamma.number%1);
  }  
}
// Double parameter 
class Time {
  int hours,minutes;
  double number,temp;

  public Time(int x,int y){
    hours= x;
    minutes=y;

    hours+=minutes/60;
    minutes%= 60;
  }
  //Single parameter 
  public Time(double input){
    number=  input;
    double temp ;


    temp=  (number%1*60*100)/100; 
    minutes= (int)temp;
    hours= (int)number-(int)number%1;

  }


  public String toString(){
    return String.format(hours+":"+minutes);
  }

}

Answer 1

这将对你有用：

从时间构造函数中删除临时变量声明，这就是为什么每次都得到0.00

public class Test {
  public static void main(String[]args){
    Time object =  new Time(20,329);
    Time gamma = new Time(20.75);
    System.out.println(object);
    System.out.println(gamma);
    System.out.println("temp:"+gamma.temp);
    System.out.println("minutes:"+gamma.minutes);
    System.out.println("number:"+gamma.number%1);
  }  
}
// Double parameter 
class Time {
  int hours,minutes;
  double number,temp;

  public Time(int x,int y){
    hours= x;
    minutes=y;

    hours+=minutes/60;
    minutes%= 60;
  }
  //Single parameter 
  public Time(double input){
    number=  input;
    temp =  (number%1*60*100)/100; 
    minutes= (int)temp;
    hours= (int)number-(int)number%1;

  }


  public String toString(){
    return String.format(hours+":"+minutes);
  }

}

Answer 2

您有一个实例变量：

double temp;

以及构造函数中的局部变量

---

您应该只有一个实例变量，而且它必须是实例变量，因为您要在main中调用gamma.temp，请删除构造函数中的下面一行

此外，我建议您使用封装（见下文）来访问类外的变量

---

解决方案

public Time(double input){
    number=  input;
    //double temp ; This should be deleted


    this.temp =  (number%1*60*100)/100; 
    minutes= (int)temp;
    hours= (int)number-(int)number%1;

}

---

有用的链接

• What is the difference between a local variable, an instance field, an input parameter, and a class field?
• How do Getters and Setters work?
• What is encapsulation?