Article Directory
First, the meaning of
Objective: The basic data types for the properties of the object includes , for each elementary data type provides a wrapper class.
| basic type | Corresponding packaging |
|---|---|
| byte | Byte |
| short | Short |
| int | Integer |
| long | Long |
| float | Float |
| double | Double |
| char | Character |
| boolean | Boolean |
Second, boxing and unboxing
Packing: The basic data type conversion to its corresponding packaging.
Unpacking: the split wrapper class corresponding to the basic data types.
2.1 Packing
2.1.1 autoboxing
int num1 = 5;
Integer num2 = num1; // 自动装箱。
2.1.2 Manual packing
int num1 = 5;
Integer num2 = new Integer(num1); // 手动装箱。
2.2 Unboxing
2.2.1 auto-unboxing
Integer num1 = new Integer(5);
int num2 = num1; // 自动拆箱。
2.2.2 Manual Unboxing
Integer num1 = new Integer(5);
int num2 = num1.intValue(); // 手动拆箱。
Third, the usual method of packaging
3.1 Type converted into other types of
Syntax: numName.xxxValue ();
| method | meaning | return value |
|---|---|---|
| byte value () | Into byte type | byte |
| intValue() | Converted to an int | int |
| long value () | Into a long type | long |
| floatValue () | Converted to a float | float |
| doubleValue() | Converted to double type | double |
| toString() | Into a String | String |
| parseInt(String s) | Strings to int | static int |
| valueOf(String s) | String into an Integer | static Integer |
Integer num1 = new Integer("5");
// 或者Integer num1 = 5;
// 或者 Integer num1 = new Integer(5);
String str = num1.toString();
3.2 Basic Data type conversion between a character string
3.2.1 into a string
A grammar: numName.toString ();
Integer num1 = new Integer("5");
String str = num1.toString();
Syntax two: String.valueOf (numName);
Integer num1 = new Integer("5");
String str = String.valueOf(num1);
Syntax three: numName + "";
Integer num1 = new Integer("5");
String str = num1 + "";
3.2.2 string into basic types
A grammar: Xxx.parseXxx (strName);
Note: encountered non-numeric stop.
String str1 = new String("123");
int num1 = Integer.parseInt(str1); // 结果：num1 = 123;
String str2 = new String("123a2");
int num2 = Integer.parseInt(str2); // 结果：num2 = 123;
String str3 = new String("123.4a2");
int num3 = Integer.parseInt(str3); // 结果：num3 = 123.4;
Syntax two: Xxx.valueOf (strName);
String str = new String("123");
int num = Integer.valueOf(str);