String方法Append（）：StringBuilder vs StringBuffer [英] String method Append() : StringBuilder vs StringBuffer

问题描述

我有这个方法，

  public static void main(String[] args) {

    String s = "Java";
    StringBuilder buffer = new StringBuilder(s);
    change(buffer);

       System.out.println("What's strBuf.charAt(5)? " + strBuf.charAt(3));
       System.out.println(buffer);
  }

     private static void change(StringBuilder buffer) {

          buffer.append(" and HTML");
  }

当我使用StringBuilder运行代码时，我收到错误消息，
构造函数StringBuilder（String）未定义
方法charAt（int）未定义类型StringBuilder

When I run the code using StringBuilder I get error message , "The constructor StringBuilder(String) is undefined The method charAt(int) is undefined for the type StringBuilder"

在调试过程中，我尝试了StringBuffer相反，它完美地工作。
StringBuffer对象的内容被编译为Java和Eclipse ..

On the proccess of debugging , I tried StringBuffer instead and it worked perfectly. The content of the StringBuffer object is compiled to "Java and Eclipse.."

  public static void main(String[] args) {

    String s = "Java";
    StringBuffer strbuf = new StringBuffer(s);
    change(strbuf);

               System.out.println("The Stringbuffer.charAt(5) is ? " + strbuf.charAt(3));
           System.out.println(strbuf);
 }

       private static void change(StringBuffer strbuf) {

                       strbuf.append(" and Eclipse");
 }
 }

有人可以告诉我为什么后者StringBuffer有效和Stringbuilder没有。
和是否合法将字符串传递给StringBuilder构造函数是合法的。 StringBuilder的（一个或多个）;

Can someone enlighten me why the latter"StringBuffer" worked and Stringbuilder didnt. and wether or not it is legal to pass the string into the in the StringBuilder constructor. "StringBuilder(s);"

推荐答案

StringBuilder 有一个构造函数接受字符串作为参数， 一个 .charAt（）方法（它必须实现它，因为它实现了 CharSequence ）。

StringBuilder does have a constructor accepting a String as an argument, and does have a .charAt() method (which it it must implement since it implements CharSequence).

结论：这是IDE部分的一个不幸事件，它没有导入正确的的StringBuilder 。你使用另一个库，它有一个不幸的属性，它实现了一个同名的类 - 但不是在同一个包中。

Conclusion: this is a mishap from the part of your IDE, which did not import the correct StringBuilder. You use another library which has the unfortunate "property" of having implemented a class by the same name -- but not in the same package.

去看看顶部你的文件，如果导入行是：

Go see at the top of your file if the import line is:

import java.lang.StringBuilder;

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