在java中反射数组 [英] Reflection of an array in java

问题描述

我对Java很新，遇到了一个问题。我的任务是创建一个类，它包含一个方法write（Object obj），它将对象的类型以及所有属性的名称和类型写入文件。涉及到递归，因为对象可能将对象/对象数组作为属性。

这是代码：

  public void write（Object obj）throws Exception {
 
 if（obj == null）
 {
 out.close（）; 
返回; 
} 
 
类c = obj.getClass（）; 
 D类; 
 Field fields_c [] = c.getDeclaredFields（）; 
 System.out.println（class_name：+ c.getName（））; 
 
 int i，j; 
 String tab = new String（）; 
 
 
 for（i = 0; i< indent_level; i ++）
 {
 tab = tab +\t; 
} 
 
 out.write（tab +class_name：+ c.getName（）+\\\
）;对于（i = 0; i< fields_c.length; i ++）{
 System.out.println（field name：+ fields_c [i] .getName（）+）的
 
 ）; 
 
 c = fields_c [i] .getType（）; 
 fields_c [i] .setAccessible（true）; 
 
 if（c.isPrimitive（））{
 out.write（\t+ tab +field_name：+ c.toString（）+\\\
） ; 
} 
 else if（c.isArray（））{
 System.out.println（array of type with types of type：+ c.getComponentType（））; 
 
 for（j = 0; j< Array.getLength（c）; j ++）
 {
 d = Array.get（c，j）.getClass（）; 
 indent_level = indent_level + 1; 
 this.write（d）; 
 indent_level = indent_level  -  1; 
} 
} 
 else 
 {
 System.out.println（field is not primitive of type：+ c.getName（））; 
对象foo = fields_c [i] .get（obj）; 
 indent_level = indent_level + 1; 
 this.write（foo）; 
 indent_level = indent_level  -  1; 
} 
} 
} 
  

如果我打电话该方法并给出具有数组属性的Object;所有属性，直到数组正确写入输出文件。
异常是java.lang.IllegalArgumentException：Argument不是数组。

解决方案

在 d = Array.get（c，j）.getClass（）; c 类型为java.lang.Class，但是您应该将其更改为 d = Array.get（fields_c [i] .get（obj），j）

并使用 c＃getComponentType 获取数组的类型。

I'm fairly new to java and have come across a problem. My task is to create a class which contains a method write(Object obj) that writes the type of the object as well as the name and type of all attributes into a file. Recursion is involved since the object may have objects/arrays of objects as attributes.

Here is the code:

    public void write(Object obj) throws Exception {

    if(obj == null)
    {
        out.close();
        return;
    }

    Class c = obj.getClass();
    Class d;
    Field fields_c[] = c.getDeclaredFields();
    System.out.println("class_name:" + c.getName());

    int i, j;
    String tab = new String("");


    for(i = 0; i < indent_level; i++)
    {
        tab = tab + "\t";
    }

    out.write(tab + "class_name:" + c.getName() + "\n");

    for(i = 0; i < fields_c.length; i++) {
        System.out.println("field name: " + fields_c[i].getName() + " ");

        c = fields_c[i].getType();
        fields_c[i].setAccessible(true);

        if(c.isPrimitive()) {
            out.write("\t" + tab + "field_name:" + c.toString() + "\n");
        }
        else if(c.isArray()) {
            System.out.println("field of type array with elements of type:" + c.getComponentType());

            for(j = 0; j < Array.getLength(c); j++)
            {
                d = Array.get(c, j).getClass();
                indent_level = indent_level + 1;
                this.write(d);
                indent_level = indent_level - 1;            
            }
        }
        else
        {
            System.out.println("field is not primitive of type:" + c.getName());
            Object foo = fields_c[i].get(obj);
            indent_level = indent_level + 1;
            this.write(foo);
            indent_level = indent_level - 1;
        }
    }
}

An exception arises if I call the method and give an Object that has an array attribute; all attributes until the array are written properly to the output file. The exception is "java.lang.IllegalArgumentException: Argument is not an array".

解决方案

In d = Array.get(c, j).getClass(); c is of type java.lang.Class, but an array is expected.

You should change it to d = Array.get(fields_c[i].get(obj), j) and use c#getComponentType for get the type of the array.

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