And basic operation of the digital string

Basic Operation digital string

Unpacking Packing

Unpacking : converting the package type by assigning a basic type.

Integer i = new Integer(12);
//类类型转换为基本类型
int i2 = i.intValue();
//自动拆箱
int i3 = i;

Packing : converting the base type by assigning class type.

int i = 12;
//基本类型转换为类类型
Integer it1 = new Integer(i);
//自动装箱
Integer it2 = i;

String and numeric conversion

//数字转字符串
int i = 12;
//使用valueOf
String str1 = String.valueOf(i);
//装箱后使用数字封装类对象的toString
Integer it = i;
String str2 = it.toString();

//字符串转数字，调用Integer的静态对象parseInt
String str = "999";
int i = Integer.parseInt(str);

A common method of character classes

Character.isLetter('a');
Character.isDigit('a');
Character.isWhitespace(' ');
Character.isUpperCase('A');
Character.isLowerCase('a');
Character.toUpperCase('a');
Character.toLowerCase('A');

//字符转换为字符串，调用字符类的toString
String a = Character.toString('a');
//字符串转换为字符数组，调用字符串对象的toCharArray()
char[] cs = str.toCharArray();