int -> String
String s=String.valueOf(12345);
String -> int
int i=Integer.parseInt("123");
String->char
"12345".charAt(index) 傳回位置在index的char
String->char[ ]
"12345".toCharArray() 傳回整個char[ ]
char->String
String s=String.valueof('c');
char[ ]->String
String s = String.valueOf(new char[]{'c','b'});