java 字符串缓冲区声明

Question

当我不包含注释行时，prevLineBuffer 包含“null”。当我包含注释行时，它仍然有效，但打印一个空字符串。 Java 是否为声明的字符串静态分配空间，然后为注释行中的附加字符串动态分配空间？两者似乎都有效...

public class Indexer {
    String input;
    StringBuilder prevLineBuffer;

    Indexer(String inputFileName) throws RuntimeException{
        input = inputFileName;
        //prevLineBuffer = new StringBuilder();
        System.out.print(prevLineBuffer);

    }//constructor
}//class

Answer 1

您需要打印 .toString() 的结果，并为其添加 .append() 内容，以便为其提供打印内容。例如:

    prevLineBuffer = new StringBuilder();
    prevLineBuffer.append(inputFileName);
    System.out.print(prevLineBuffer.toString());

回答你问题的后半部分......

来自String docs :

A pool of strings, initially empty, is maintained privately by the class String. [...] When the intern method is invoked, if the pool already contains a string equal to this String object as determined by the equals(Object) method, then the string from the pool is returned. Otherwise, this String object is added to the pool and a reference to this String object is returned.

来自StringBuilder docs :

In general, if sb refers to an instance of a StringBuilder, then sb.append(x) has the same effect as sb.insert(sb.length(), x). Every string builder has a capacity. As long as the length of the character sequence contained in the string builder does not exceed the capacity, it is not necessary to allocate a new internal buffer. If the internal buffer overflows, it is automatically made larger. -