使用Reflect变态修改String值的方法。_reflect field 修改-优快云博客

本文链接：https://blog.youkuaiyun.com/flyforlove/article/details/1133364

本文介绍了一种利用Java反射机制实现字符串修改和交换的方法。通过直接操作字符串内部的`offset`、`count`和`value`字段，可以实现字符串内容的替换与两个字符串变量之间的值交换。该方法突破了字符串不可变性的限制，但需谨慎使用。

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import java.lang.reflect.Field;

public class ModifyStr {

public static void ModifyString(String s){
  String tmp = "想改就改，怎么着吧";
  Class cls = s.getClass();

   try {
    Field offset = cls.getDeclaredField("offset");
   offset.setAccessible(true);
   offset.setInt(s, 0);

   Field count = cls.getDeclaredField("count");
   count.setAccessible(true);
   count.setInt(s, tmp.length());

   Field value = cls.getDeclaredField("value");
   value.setAccessible(true);
   value.set(s, tmp.toCharArray());
  } catch (SecurityException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  } catch (NoSuchFieldException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  } catch (IllegalArgumentException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  } catch (IllegalAccessException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }

}

public static void main(String[] args){
  // TODO Auto-generated method stub
  String s = "什么都行";
  ModifyString(s);
  System.out.println(s);
}

}

import java.lang.reflect.Field;
public class SwapString {
public void swap(String str1, String str2){
  String tmpStr = new String(str1);
  Class cls = String.class;

  try {
   Field offset = cls.getDeclaredField("offset");
      Field count = cls.getDeclaredField("count");
      Field value = cls.getDeclaredField("value");

      offset.setAccessible(true);
      count.setAccessible(true);
      value.setAccessible(true);

      offset.setInt(str1, 0);
      count.setInt(str1, str2.length());
      value.set(str1, str2.toCharArray());

      offset.setInt(str2, 0);
      count.setInt(str2, tmpStr.length());
      value.set(str2, tmpStr.toCharArray());
  } catch (SecurityException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  } catch (NoSuchFieldException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  } catch (IllegalArgumentException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  } catch (IllegalAccessException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
}
public static void main(String[] args) {
  SwapString ss = new SwapString();
  String s1 = "String1";
  String s2 = "String2";
  System.out.println("Before Swap :/n s1 = "+s1+", s2 = "+s2);
  ss.swap(s1, s2);
  System.out.println("After Swap :/n s1 = "+s1+", s2 = "+s2);
}