#String

基本

substring(a,b) 左闭右开

StringBuilder / StringBuffer 在后面添加使用 或者insert(index,char)

s.append("s")

StringBuffer 与 StringBuilder, 前者保证线程安全，后者不是，但单线程下效率高一些，一般使用 StringBuilder.

StringBuilder / StringBuffer 变成String 用

sb.toString()

String 变成CharArray

char[] s2Char = s2.toCharArray()

• StringBuilder / StringBuffer 的话 String

CharArray to String 用

chars[index] = c;
String s =  new String(chars);

Integer to string

Integer.toString(i)

Integer to Char

- integer转化为char(只限于0-9) char key = (char) ('0' + k);

String s1 = new String();
String s2 = "billryan";
int s2Len = s2.length();
s2.substring(4, 8); // return "ryan"
StringBuilder sb = new StringBuilder(s2.substring(4, 8));
sb.append("bill");
String s2New = sb.toString(); // return "ryanbill"
// convert String to char array
char[] s2Char = s2.toCharArray();
// char at index 4
char ch = s2.charAt(4); // return 'r'
// find index at first
int index = s2.indexOf('r'); // return 4. if not found, return -1

####替换String中的一个char

• 不能直接替换 如这样，charAt只能得到值，不能set

String myName = "domanokz";
myName.charAt(4) = 'x';

• 只能这样

String myName = "domanokz";
String newName = myName.substring(0,4)+'x'+myName.substring(5);

或者

StringBuilder myName = new StringBuilder("domanokz");
myName.setCharAt(4, 'x');