android - 继续在构造函数上出现 NullPointerException 错误

Question

我目前正在将 Java 程序转换为 Android 程序，但一直出现此错误。我在过去几天尝试转换它，但我被困在这里

日志:

03-24 01:18:21.289: E/AndroidRuntime(2329): FATAL EXCEPTION: main
03-24 01:18:21.289: E/AndroidRuntime(2329): Process: com.example.ocrtry, PID: 2329
03-24 01:18:21.289: E/AndroidRuntime(2329): java.lang.NullPointerException
03-24 01:18:21.289: E/AndroidRuntime(2329):     at com.example.ocrtry.Entry2.downSample(Entry2.java:231)
03-24 01:18:21.289: E/AndroidRuntime(2329):     at com.example.ocrtry.MainActivity$1.onClick(MainActivity.java:42)

第 231 行:data = sample.getData();

这是 Entry2.downSample 的代码 fragment :

protected Sample sample;
public void downSample()
{
  int w = bmInput.getWidth();
  int h = bmInput.getHeight();
  int[] pixels = new int[bmInput.getWidth() * bmInput.getHeight()];
  bmInput.getPixels(pixels, 0, w, 0, 0, w, h);
  pixelMap = (int[])pixels;
  findBounds(w, h);
  SampleData data;
  data = sample.getData();

  ratioX = (double) (downSampleRight - downSampleLeft) / (double) data.getWidth();
  ratioY = (double) (downSampleBottom - downSampleTop) / (double) data.getHeight();

  for (int y = 0; y < data.getHeight(); y++)
  {
     for (int x = 0; x < data.getWidth(); x++)
     {
        if (downSampleQuadrant(x, y))
           data.setData(x, y, true);
        else
           data.setData(x, y, false);
     }
  }
}

下面是示例类的代码:

public class Sample
{

  //The image data.
  SampleData data;
  /**
  * The constructor.
  * 
  * @param width
  *          The width of the downsampled image
  * @param height
  *          The height of the downsampled image
  */
  Sample(int width, int height)
  {
    data = new SampleData(' ', width, height);
  }

 /**
 * The image data object.
 * 
 * @return The image data object.
 */
  SampleData getData()
  {
    return data;
  }

 /**
 * Assign a new image data object.
 * 
 * @param data
 *          The image data object.
 */
  void setData(SampleData data)
  {
    this.data = data;
  } 
}

SampleData 的代码:

public class SampleData
{

  //The downsampled data as a grid of booleans.
  protected boolean grid[][];

  protected char letter;

  /**
  * The constructor
  * 
  * @param letter
  *          What letter this is
  * @param width
  *          The width
  * @param height
  *          The height
  */
 public SampleData(char letter, int width, int height)
  {
    grid = new boolean[width][height];
    this.letter = letter;
  }

  /**
  * Set one pixel of sample data.
  * 
  * @param x
  *          The x coordinate
  * @param y
  *          The y coordinate
  * @param v
  *          The value to set
  */
  public void setData(int x, int y, boolean v)
  {
    grid[x][y] = v;
  }

  /**
  * Get a pixel from the sample.
  * 
  * @param x
  *          The x coordinate
  * @param y
  *          The y coordinate
  * @return The requested pixel
  */
  public boolean getData(int x, int y)
  {
    return grid[x][y];
  }

  public void clear()
  {
    for (int x = 0; x < grid.length; x++)
      for (int y = 0; y < grid[0].length; y++)
        grid[x][y] = false;
  }
  public int getHeight()
  {
    return grid[0].length;
  }
  public int getWidth()
  {
    return grid.length;
  }
  public char getLetter()
  {
    return letter;
  }
  public void setLetter(char letter)
  {
    this.letter = letter;
  }
  public int compareTo(Object o)
  {
    SampleData obj = (SampleData) o;
    if (this.getLetter() == obj.getLetter())
      return 0;
    else if (this.getLetter() > obj.getLetter())
      return 1;
    else
      return -1;
  }

  public boolean equals(Object o)
  {
    return (compareTo(o) == 0);
  }
  public String toString()
  {
    return "" + letter;
  }
  public Object clone()

  {
    SampleData obj = new SampleData(letter, getWidth(), getHeight());
    for (int y = 0; y < getHeight(); y++)
      for (int x = 0; x < getWidth(); x++)
        obj.setData(x, y, getData(x, y));
    return obj;
  }

}

Answer 1

  SampleData data;
  data = sample.getData();

您首先需要一个 SampleData 实例。

 SampleData getData()
  {
    return data;
  }

不创建它的实例。

也许这样的事情可以工作:调用如下:

     SampleData data;
  data = sample.getData(w,h);

然后在 SampleData 类中:

 SampleData getData(int width, int height)
  {
    data = new SampleData(width, height);
    return data;
  }