NullPointerException in AbstractTableModel getRowCount

Question

我有一个按钮，它只读取数据库表中的所有字段(从电影中选择*)，所以我使用AbstractTableModel。第一个表用这个类读取OK，但是如果我为其他表实现AbstractTableModel，则得到NPE。

下面是我的代码TableModelForMovies：

package ua.movies.movie;

import java.util.ArrayList;
import java.util.List;

import javax.swing.table.AbstractTableModel;

public class TableModelForMovies extends AbstractTableModel {

    private static final int NAME_COL = 0;
    private static final int Genre_COL = 1;
    private static final int Release_Date = 2;
    private static final int Unique = 3;

    private String[] columnNames = { "name", "genre", 
    "release" , "dgdggdf" };

    private List<Movie> movies;

     public TableModelForMovies(List<Movie> theMovie) {
        movies = theMovie;
    }

    @Override
    public int getRowCount() {
        return movies.size(); <<- here is problem
    }

    @Override
    public int getColumnCount() {
        return columnNames.length;
    }

    @Override
    public String getColumnName(int col) {
        return columnNames[col];
    }

    @Override
    public Object getValueAt(int rowIndex, int columnIndex) {
        Movie tmpMovie = movies.get(rowIndex);
        switch (columnIndex) {
        case NAME_COL:
            return tmpMovie.getMovieName();
        case Genre_COL:
            return tmpMovie.getGenre();     
        case Release_Date: 
            return tmpMovie.getRelease();
        case Unique: 
            return tmpMovie.getUniqueKey();

        default:
            return tmpMovie.getMovieName();
        }
    }
}

我按钮上的听者

try {
    String movieName  = textFindField.getText();
    List<Movie> employees = null;
    if (movieName != null && movieName.trim().length() > 0) {
        //employees = movieDao.search(lastName);
        employees = movieDao.getAllMovies();
    } else {
        searchByName();
    }

    // create the model and update the "table"
    TableModelForMovies model = new TableModelForMovies(employees);

    tableMovies.setModel(model);
} catch (Exception exc) {
    JOptionPane.showMessageDialog(AppMovies.this, "Error: " + exc, "Error", JOptionPane.ERROR_MESSAGE); 
}

我真的不明白为什么我有NPE。因为我有第二类，它也扩展了AbstractTableModel，没有任何错误，NPE就在这里。

Answer 1

可能在初始化getRowCount()列表之前调用movies方法，当您重写getRowCount()方法时，请使用以下模式：

 @Override
  public int getRowCount()
  {
    int result = 0;
    synchronized(LOCK) {
      if(movies != null) {
        result = movies.size();
      } // if
    } // synchronized
    return result;
  }