我要替换str里的str2,换成str3里的词， 为什么我的程序会瘫痪呢？

   public String replaceSubstring()
    {
        StringBuilder str=new StringBuilder(line);
        String str2="the";
        String str3="that";
        int position;
        
        position = str.indexOf(str2);
        str.replace(position,position+str2.length(), str3);
        while (position !=-1)
        {
            position = str.indexOf(str2, position+1);
            str.replace(position,position+str2.length(), str3);
        }
            
        return str.toString();
    }

        

        String str="the aaga asgagathe"; 
                 
        String str2="the"; 
        String str3="that"; 
 
        str=str.replace(str2, str3); 
         
        System.out.println(str);

这种方法是很简单,但是要求是不可以用这个方法, 需要用我的方法,大家帮我改一下我的程序

//自己去总结吧。
import java.lang.StringBuilder;
class replace1{
    public String replaceSubstring()
      {
            StringBuilder str=new StringBuilder("cat is cat");
            String str2="cat";
            String str3="dog";
            int position;
            
            position = str.indexOf(str2);
      
          str.replace(position,position+str2.length(), str3);
 
            while (position !=-1)
            {
                 
                position = str.indexOf(str2, position+1);
                if(position==-1){
                    break;
                }else{
                    str.replace(position,position+str2.length(), str3);
                }
               
            }
                return str.toString();
 
        }
}
public class Dancitihuan {
 
    public static void main(String[] args) {
        replace1  re=new replace1();
        System.out.println(re.replaceSubstring());
      
    }
 
}

楼主，你是要转换“the”单词还是字符，如果是前者就要用正则表达式“\\bthe\\b”，因为很多英文单词里都包含"the"字符串, 如"weather"