java - 变量只在 while 循环内才有值？

Question

static void parse(String fileName) throws IOException{
    FileReader fileReader=new FileReader((fileName));
    BufferedReader bufferedReader = new BufferedReader(fileReader);
    StringBuilder stringBuilder=new StringBuilder();
    String string;
    StringBuilder myString = null;
    while((string = bufferedReader.readLine()) != null) {                
        myString =stringBuilder.append(string);
        String h=myString.toString();
        **System.out.println(h);**
        }

    }




static void parse(String fileName) throws IOException{
    FileReader fileReader=new FileReader((fileName));
    BufferedReader bufferedReader = new BufferedReader(fileReader);
    StringBuilder stringBuilder=new StringBuilder();
    String string;
    StringBuilder myString = null;
    while((string = bufferedReader.readLine()) != null) {                 
        myString =stringBuilder.append(string);
        String h=myString.toString();
       }

       **System.out.println(h);**  
    }

当我尝试代码的第二部分时，它什么也没打印出来。如何在 while 循环之外获取整个 h 字符串？我是否必须将变量 h 声明为实例变量而不是局部变量？

Answer 1

无需创建实例变量。只需将 h 放在循环之外即可:-

static void parse(String fileName) throws IOException{
FileReader fileReader=new FileReader((fileName));
BufferedReader bufferedReader = new BufferedReader(fileReader);
StringBuilder stringBuilder=new StringBuilder();
String string,h=null;
StringBuilder myString = null;
while((string = bufferedReader.readLine()) != null) {                
    myString =stringBuilder.append(string);
    h=myString.toString();
    }
   System.out.println(h);
}