StringBuilder vs StringBuffer

Initialization

StringBuilder

// 在单线程更高效，但在多线程中不安全
everything is as same as StringBuffer

StringBuffer

// 在多线程更好，但不够高效，在多线程中更安全
// 加了lock功能，防止多线程同时修改某个string引起conflict
StringBuffer s = new StringBuffer();
// original capacity is 16, length is 0

StringBuffer s = new StringBuffer("abc");
/// current capactity is 16+3, length is 3

s.append("de")
// current capacity is 19, length is 3+2

Useful methods

StringBuilder

// Some code

StringBuffer

s.append("ccd");   // s is updated