一、創建Stringbuilder對象
StringBuilder strB = new StringBuilder();
1、append(String str)/append(Char c)：字符串連接
System.out.println("StringBuilder:"+strB.append("ch").append("111").append('c'));
//return "StringBuilder:ch111c"
2、toString()：返回一個與構建起或緩沖器內容相同的字符串
System.out.println("String:"+strB.toString());
//return "String:ch111c"
3、appendcodePoint(int cp)：追加一個代碼點，並將其轉換為一個或兩個代碼單元並返回this
System.out.println("StringBuilder.appendCodePoint:"+strB.appendCodePoint(2));
//return "StringBuilder.appendCodePoint:ch111c"
4、setCharAt(int i, char c)：將第 i 個代碼單元設置為 c（可以理解為替換）char字符使用 ‘ ’
strB.setCharAt(2, 'd');
System.out.println("StringBuilder.setCharAt:" + strB);
//return "StringBuilder.setCharAt:chd11c"
5、insert(int offset, String str)/insert(int offset, Char c)：在指定位置之前插入字符(串)
System.out.println("StringBuilder.insertString:"+ strB.insert(2, "LS"));
//return "StringBuilder.insertString:chLSd11c"
System.out.println("StringBuilder.insertChar:"+ strB.insert(2, 'L'));
//return "StringBuilder.insertChar:chLLSd11c"
6、delete(int startIndex,int endIndex)：刪除起始位置（含）到結尾位置（不含）之間的字符串
System.out.println("StringBuilder.delete:"+ strB.delete(2, 4));
//return "StringBuilder.delete:chSd11c"