e070. constructing a string.txt

这里面包含了一百多个JAVA源文件

If you are constructing a string with several appends, it may be more efficient to construct it using a StringBuffer and then convert it to an immutable String object. 
    StringBuffer buf = new StringBuffer("Java");
    
    // Append
    buf.append(" Almanac v1/");      // Java Almanac v1/
    buf.append(3);                   // Java Almanac v1/3
    
    // Set
    int index = 15;
    buf.setCharAt(index, '.');       // Java Almanac v1.3
    
    // Insert
    index = 5;
    buf.insert(index, "Developers ");// Java Developers Almanac v1.3
    
    // Replace
    int start = 27;
    int end = 28;
    buf.replace(start, end, "4");    // Java Developers Almanac v1.4
    
    // Delete
    start = 24;
    end = 25;
    buf.delete(start, end);          // Java Developers Almanac 1.4
    
    // Convert to string
    String s = buf.toString();