java - 如何根据程序启动时生成的数据初始化全局矩阵？

Question

我正在创建一个程序，它必须保存许多信息，其中一个存储一个矩阵，其中的想法是保留 0 或 -1，具体取决于该项目是否存在 (0)，否则为 (-1)。但是当我尝试在方法中初始化这个矩阵时，会生成 nullPointerException。

我尝试像这样初始化矩阵来修复它:

public static int libros[][]= new int[arrayListLibros.size()][numeroMayor()];

但它会产生另一个错误

Exception in thread "main" java.lang.ExceptionInInitializerError
at Modelo.Main.main(Main.java:26)
Caused by: java.lang.NullPointerException
at Modelo.SistemaDeGestion.<clinit>(SistemaDeGestion.java:19)
... 1 more

没找到解决办法

这是代码:

    public void cargarMatrizLibros() throws Exception{
    int numeroMayor = numeroMayor();
    for (int j = 0; j < arrayListLibros.size(); j++){
        for (int k = 0; k < numeroMayor; k++){
            if( k < Integer.getInteger(arrayListLibros.get(j).getEjemplares())){
                libros[j][k] = 0;
            }
            else{
                libros[j][k] = -1;
            }
        }
    }
}

public static int numeroMayor(){
    int numeroMayor = 0;
    for (int i = 0; i < arrayListLibros.size(); i++) {
        if(Integer.getInteger(arrayListLibros.get(i).getEjemplares()) > numeroMayor){
            numeroMayor = Integer.getInteger(arrayListLibros.get(i).getEjemplares());
        }
    }
    return numeroMayor;
}

arrayListLibros 之前已在程序的 main 方法中初始化:

SistemaDeGestion sistema = new SistemaDeGestion();
    try {
        sistema.cargarDatosEmpleados();
        sistema.cargarDatosUsuarios();
        sistema.cargarDatosLibros();
        sistema.cargarMatrizLibros();
    } catch (Exception ex) {
        Logger.getLogger(Main.class.getName()).log(Level.SEVERE, null, ex);
    }

其中 sistema 引用了创建的类...cargarDatosLibros 的代码在这里:

public void cargarDatosLibros() throws Exception {
    arrayListLibros = new ArrayList<>();
    ArrayList<String> lineas = leerArchivo("libros.txt");

    for (int i = 0; i < lineas.size(); i++) {
        String libro[] = {"", "", "", "", "", "", ""};
        int c1 = lineas.get(i).indexOf("~T");
        int c2 = lineas.get(i).indexOf("~A");
        libro[0] = lineas.get(i).substring(c1 + 2, c2);
        int c3 = lineas.get(i).indexOf("~A");
        int c4 = lineas.get(i).indexOf("~E");
        libro[1] = lineas.get(i).substring(c3 + 2, c4);
        int c5 = lineas.get(i).indexOf("~E");
        int c6 = lineas.get(i).indexOf("~Tem");
        libro[2] = lineas.get(i).substring(c5 + 2, c6);
        int c7 = lineas.get(i).indexOf("~Tem");
        int c8 = lineas.get(i).indexOf("~Edi");
        libro[3] = lineas.get(i).substring(c7 + 4, c8);
        int c9 = lineas.get(i).indexOf("~Edi");
        int c10 = lineas.get(i).indexOf("~Anho");
        libro[4] = lineas.get(i).substring(c9 + 4, c10);
        int c11 = lineas.get(i).indexOf("~Anho");
        int c12 = lineas.get(i).indexOf("~I");
        libro[5] = lineas.get(i).substring(c11 + 5, c12);
        int c13 = lineas.get(i).indexOf("~I");
        int c14 = lineas.get(i).indexOf("~End");
        libro[6] = lineas.get(i).substring(c13 + 2, c14);
        int z = i + 1;
        Libro temp = new Libro(libro[0], libro[1], libro[2], libro[3], libro[4], libro[5], libro[6], z);
        arrayListLibros.add(temp);
    }
}

所以我不知道是哪个问题，因为它之前已经初始化过。

谢谢:)

Answer 1

我猜你的arrayListLibros尚未初始化。加载类时会加载静态内容。

public static int libros[][]= new int[arrayListLibros.size()][numeroMayor()];

arrayListLibros尚未初始化，因此在调用size()时会导致NullPointerException，从而导致ExceptionInInitializerError。

来自 API:

Signals that an unexpected exception has occurred in a static initializer. An ExceptionInInitializerError is thrown to indicate that an exception occurred during evaluation of a static initializer or the initializer for a static variable.

编辑:

类似如下:

public class StaticTestForLaura {
    static List<String> arrayListLibros;
    static {
            arrayListLibros= new ArrayList<String>();
        arrayListLibros.add("Laura");
    }
    public static int libros[]= new int[arrayListLibros.size()];

}