String

constructor

String s = "abc";
String s = new String("abc");

char ch[]={ 'H','e','l','l','o','!',};
String str1=new String(ch);

frequently used method

int - s.length();
char - s.charAt(0);

boolean - s.equals("a");
boolean - s.equalsIgnoreCase(a);

String - s.replace(char old, char new);
String - s.toLowerCase();
String - s.toUpperCase();
char[] - s.toCharArray();
String - s.trim();
int - s.indexOf(char);
int - s.indexOf(str);
String[] - s.split(regex);
boolean - s.endsWith(suffix);
boolean - s.startsWith(prefix);
String - s.substring(start, end);[inclusive, exclusive)
String - s.concat("a"); //"toget".concat("her") returns "together"

compare

//该方法是对字符串内容按字典顺序进行大小比较。若当前对象比参数大则返回正整数，反之返回负整数，相等返回0。
int -  s.compareTo(s1);
int -  s.compareToIgnoreCase(String anotherString);

transition

static String - String.valueOf(boolean b)
static String - String.valueOf(char c)
static String - String.valueOf(int i)
static String - String.valueOf(long l)
static String - String.valueOf(float f)
static String - String.valueOf(double d)

//将char '8' 转换为int 8
String str = String.valueOf('8');
int num = Integer.parseInt(str);

StringBuilder vs StringBuffer

• mutable
• StringBuilder is not synchronized, not thread safe but faster.
• StringBuffer is synchronized, thread safe but slower.

constructor

new StringBuilder();
new StringBuilder(str);

frequently used methods

StringBuilder - s.append(char/str);
int - s.charAt(i);
StringBuilder - s.deleteCharAt(i);
int - s.indexOf(str);
StringBuilder - s.insert(i, char);
String - s.toString();