使用java序列化保存/加载对象数组 [英] saving/loading array of objects using java serialization

问题描述

  public class Amount implements Serializable {
 private static final long serialVersionUID = 8141477444408242243L; 
 public static Amount values1 [] [] = new Amount [10] [30]; 
 public static Amount values2 [] [] = new Amount [10] [30]; 
 public static Amount values3 [] [] = new Amount [10] [30]; 
 
 double highestValue; 
 double highestAmount; 
 double lowestAmount; 
 double lowestValue; 
 $ b $ ... 
} 
  

分钟左右，我正在寻找存储阵列的文件，并加载程序启动时的值。我尝试使用java序列化方法，并具有以下功能：

pre $ public static void loadFile（Amount [] [] arr，字符串文件名）{
尝试{
FileInputStream fis = new FileInputStream（filename）;
ObjectInputStream in = new ObjectInputStream（fis）;
arr =（Amount [] []）in.readObject（）;
in.close（）;
}
catch（Exception e）{
System.out.println（e）;
}
}

公共静态无效saveFile的（金额[] [] ARR，字符串文件名）{
尝试{
FileOutputStream中FOS =新FileOutputStream中（文件名）;
ObjectOutputStream out = new ObjectOutputStream（fos）;
out.writeObject（arr）;
out.flush（）;
out.close（）;
}
catch（IOException e）{
System.out.println（e）;


$ / code $ / pre

我这样称呼 saveFile的（值1， valueOneSaveFile）; 和的loadFile（值1， valueOneSaveFile）;

我运行了一次这个程序，把所有的数组保存到不同的文件中。这些文件已经被创建并且看起来是正确的大小。当我改变我的程序来调用loadFile函数，数组似乎没有正确初始化。我试图从数组中读取一个值（这在加载后看起来是空的）时，我得到了空指针异常。解决方案

问题出在你的LoadFile方法中。
Java按值传递参数。在对象的情况下，指针的副本被传递。
当你更新数组时：

  arr =（Amount [] []）in.readObject（）; 
  

您不更新Amount.values1数组，而是本地arr变量指向一个新数组。 / b>

您应该将方法签名更改为：

  public static Amount [并且使用它。
I have the following class, which performs some calculations to fill its static arrays.
public class Amount implements Serializable{
      private static final long serialVersionUID = 8141477444408242243L;
      public static Amount values1[][] = new Amount[10][30];
      public static Amount values2[][] = new Amount[10][30];
      public static Amount values3[][] = new Amount[10][30];

      double highestValue;
      double highestAmount;
      double lowestAmount;
      double lowestValue;

      ...
}
As the calculations take 20 minutes or so, I am looking to store the arrays on file and load the values when the program starts. I am attempting to use the java serialization method and have the following functions
public static void loadFile(Amount[][] arr, String filename){
    try {
        FileInputStream fis = new FileInputStream(filename);
        ObjectInputStream in = new ObjectInputStream(fis);
        arr = (Amount[][])in.readObject();
        in.close();
      }
      catch (Exception e) {
          System.out.println(e);
      }
}

public static void saveFile(Amount[][] arr, String filename){
     try {
         FileOutputStream fos = new FileOutputStream(filename);
         ObjectOutputStream out = new ObjectOutputStream(fos);
         out.writeObject(arr);
         out.flush();
         out.close();
      }
      catch (IOException e) {
          System.out.println(e); 
      }
}
which I call like this saveFile(values1, "valueOneSaveFile"); and loadFile(values1, "valueOneSaveFile");

I have run the program once, saving all the arrays to various files. The files have been created and look to be around the correct size. When I change my program to call the loadFile functions, the arrays do not appear to initialize correctly. I am getting null pointer exceptions when trying to read a value from the array (which appears to be empty after the load)
解决方案
The problem is in your LoadFile method.
Java passes parameters by value. In the case of objects a copy of the "pointer" is passed.
When you update the array:
arr = (Amount[][])in.readObject();
You are not updating Amount.values1 array, instead the local arr variable points to a new array.

You should change the method signature to:
public static Amount[][] loadFile(String filename)
And use it accordingly.

                        
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