爪哇12小时制（上午/下午）

Question

此类ClockDisplay实现12小时数字时钟

     public class NumberDisplay
  {
 //instance variables
 private int state;
 private int limit;

 public NumberDisplay(int rollOverLimit)
 {
    state = 0;
    setLimit(rollOverLimit);
 }

   public int getState()
 {
        return state;
 }

 public int getLimit()
 {
        return limit;
 }

    public void setState(int replacementValue)
 {
    if( replacementValue >= 0 && replacementValue < limit)
        state = replacementValue;
 }

    public void setLimit(int rollOverLimit)
 {
   // if (rollOverLimit > 0)
     //   limit = rollOverLimit;


   limit = (rollOverLimit > 0 ? rollOverLimit : limit);

   state = ( state > limit ? 0 : state);

  }//of setLimit


  public void increment()
  {
    /*
    if (state == limit-1)
        state = 0;
    else
        state++;
      */  
    state = (state+1) % limit;    
    }


   public String getDisplayValue()
    {
    if(state < 10){
        return "0" + state;
    }
    else{
        return ""+ state;
    }
  }


   }

   public class ClockDisplay {

  // instance variables
  private NumberDisplay hours;
   private NumberDisplay minutes;
   private String displayString;
   private boolean isAM;
   public String displayAMPM;

    //    private int count = 0;
    public ClockDisplay() {
    hours = new NumberDisplay(12);
    minutes = new NumberDisplay(60);
    updateDisplay();
    }

    public ClockDisplay(int hour, int minute, String displayAMPM) {

    hours = new NumberDisplay(12);
    minutes = new NumberDisplay(60);
    setTime(hour, minute, displayAMPM);
    //setMorning(isAM);
    //count = 0;
    updateDisplay();
    }

    public void timeTick() {

    minutes.increment();
    if (minutes.getState() == 0) {
        hours.increment();
    }

    if (hours.getState() == 12) {
        if (displayAMPM == "AM") {
            displayAMPM = "PM";
        } else if (displayAMPM == "PM") {
            displayAMPM = "AM";
        }
    }
    //if (isAM != isAM)
    //displayAMPM = "PM";

    updateDisplay();

    }//of timeTick

    public void setTime(int hour, int minute, String displayAMPM) {
    if (hour == 12) {
        hour = 0;
    }
    hours.setState(hour);
    minutes.setState(minute);
    updateDisplay();
    }

    public void setHours(int hour) {
    hours.setState(hour);
    updateDisplay();
    }

    public void setMinutes(int minute) {
    minutes.setState(minute);
    updateDisplay();
    }
   /*public void setMorning(boolean isAM)
     {
    isAM = true;
    displayAMPM = "AM";
     }
    public void setAfternoon(boolean isAM)
    {
    isAM = false;
    displayAMPM = "PM";
 }
 */

private void updateDisplay() {
    int hour = hours.getState();
    if (hour == 0) {
        hour = 12;
    }

    displayString = hour + ":" + minutes.getDisplayValue() + displayAMPM;

  }

public String getTime() {

    return displayString;
}
}

public class Tester {

public static void main(String[] args) throws Exception {
    ClockDisplay clock12 = new ClockDisplay(11, 59, "AM");
    System.out.println(clock12.displayAMPM);
    System.out.println(clock12.getTime());
    while (true) {
        Thread.currentThread().sleep(60000);
        clock12.timeTick();
        System.out.println(clock12.getTime());
    }
 }
}

上述程序为12小时制，显示AM/PM 如果我输入“AM”或“PM”，变量displayAMPM将被视为null

Output: null
        11:59null
        12.00null

我不确定这个节目出了什么问题。有人能帮我吗

Answer 1

您永远不会在初始化时更改displayAMPM的值。在本例中，您应该在构造函数中，在您调用的方法中执行此操作：

public void setTime(int hour, int minute, String displayAMPM) {
    if (hour == 12) {
        hour = 0;
    }
    hours.setState(hour);
    minutes.setState(minute);
    this.displayAMPM = displayAMPM; // 'this.displayAPMP' will refer 
                                    // to the instance attribute 'displayAMPM'
    updateDisplay();
}

另外，不要使用==运算符来比较字符串。因为它们是对象，并且您想要比较其内容（而不是其引用），所以应该使用.equals()

Answer 2

我认为在调用构造函数时您并没有设置displayAMPM字符串

根据我的意见，在调用构造函数时必须初始化该字符串，否则它将不会设置为小时。getState（）=“12”您已经检查了以前从未设置的值，因此它不会设置为任何值

希望这个建议对你有帮助