数组初始化的 NullPointerException 错误（Java）

Question

当我尝试运行该程序时，出现以下错误：

Exception in thread "main" java.lang.NullPointerException at TemperatureMonth.getMaxTempWeekly(TemperatureMonth.java:25) at runner_TemperatureMonth.main(runner_TemperatureMonth.java:41)

我尝试将字段变量周初始化为二维数组温度的长度，但没有成功。

我只是想弄清楚这个错误到底是什么，以及以后如何避免它。

如果修复 NullPointerException 后有任何错误，我可以自己修复。

也许看看最后一个方法，我在删除返回新的二维数组温度后开始出现错误

{

  private double[][] temperatures;
  private double[] week;
  private double[] week_low;
  private double[] week_high;

  public TemperatureMonth(double[][] t)
  {
    temperatures = t;
  }`
`
  `public double[] getMaxTempWeekly()
  {
    // Remove return and implement getMaxTempWeekly method here
    double high;
    for (int x = 0; x < temperatures.length; x++) {
      high = temperatures[x][0];
      for (int y = 0; y < temperatures[0].length; y++) {
        if (temperatures[x][y] > high) {
          high = temperatures[x][y];
        }
      }
      week[x] = high;
    }
    return week;
  }`

 ` public double[] getMinTempWeekly()
  {
    // Remove return and implement getMinTempWeekly method here
    double high;
    for (int x = 0; x < temperatures.length; x++) {
      high = temperatures[x][0];
      for (int y = 0; y < temperatures[0].length; y++) {
        if (temperatures[x][y] < high) {
          high = temperatures[x][y];
        }
      }
      week[x] = high;
    }
    return week;
  }`
  
  public double getRange()
  {
    // Remove return and implement getRange method here`

    double high;
    double low;
    for (int x = 0; x < temperatures.length; x++) {
      high = temperatures[x][0];
      low = temperatures[x][0];
      for (int y = 0; y < temperatures[0].length; y++) {
        if (temperatures[x][y] > high) {
          high = temperatures[x][y];
        }
        else if (temperatures[x][y] < low) {
          low = temperatures[x][y];
        }
      }
      
      week_high[x] = high;
      week_low[x] = low;
    }
    
    double max = week_high[0];
    double min = week_low[0];
    for (int x = 0; x < week_high.length; x++) {
      if (week_high[x] > max) {
        max = week_high[x];
      }
      if (week_low[x] < min) {
        min = week_low[x];
      }
    }
    
    return max - min;
  }

  `public double getCertainTemp(int week, int day)
  {
    // Remove return and implement getCertainTemp method here`
    
    double number  = temperatures[week][day];
    return number;
  }

}`