1.概念
基本数据类型所对应的对象类型
2.类型匹配
基本数据类型 | 对应的对象类型 |
byte | Byte |
short | Short |
int | Integer |
long | Long |
float | Float |
double | Double |
boolean | Blooean |
char | Character |
3.优点
(1)作为对象类型的数据可以被Object类统一管理
(2)包装类的默认值为:null 可以有效的区分有和无
(3)支持缓存,节省空间
4.常用方法
(1)基本数据类型转换为包装类型
<1>构造方法转换:
public class IntegerToInt01 {
public static void main(String[] args) {
// TODO Auto-generated method stub
//1.构造方法转换
//int->Integer
Integer int01=new Integer(10);
System.out.println(int01);
//byte->Byte
Byte by01=new Byte((byte)20);
System.out.println(by01);
//double->Double
Double db01=new Double(20.0);
System.out.println(db01);
//long->Long
Long lg01=new Long(100);
System.out.println(lg01);
//boolean->Boolean
Boolean bl=new Boolean(true);
System.out.println(bl);
//char->Character
Character ch01=new Character('A');
System.out.println(ch01);
}
}
<2>valueOf方法转换
public class IntegerToInt02 {
public static void main(String[] args) {
//2.valueOf方法转换
//int->Integer
Integer in01=Integer.valueOf(10);
System.out.println(in01);
//byte->Byte
Byte by01=Byte.valueOf((byte) 127);
System.out.println(by01);
//short->Short
Short sh01=Short.valueOf((short) 32767);
System.out.println(sh01);
//long->Long
Long long01=Long.valueOf(2147483647);
System.out.println(long01);
//float->Float
Float fl01=Float.valueOf((float) 12.2);
System.out.println(fl01);
//double ->Double
Double db01=Double.valueOf(12.22);
System.out.println(db01);
//boolean->Boolean
Boolean bl=Boolean.valueOf(false);
System.out.println(bl);
//char->Character
Character ch01=Character.valueOf('A');
System.out.println(ch01);
}
}
(2)包装类型转换为基本数据类型
格式:
public xxx xxValue();
xxx:目标类型
xx:目标类型名称
public class IntegerToInt03 {
public static void main(String[] args) {
// TODO Auto-generated method stub
//包装类型转换为基本数据类型
//1.Integer->int
Integer int01=Integer.valueOf(12);
int int02=int01.intValue();
System.out.println(int02);
//2.Byte->byte
Byte by01=Byte.valueOf((byte) 127);
byte by02=by01.byteValue();
System.out.println(by02);
//3.Short->short
Short sh01=Short.valueOf((short) 214755);
short sh02=sh01.shortValue();
System.out.println(sh02);
//4.Long->long
Long lg01=Long.valueOf(124511);
long lg02=lg01.longValue();
System.out.println(lg02);
//5.Float->float
Float ft01=Float.valueOf((float) 12.2);
float ft02=ft01.floatValue();
System.out.println(ft02);
//6.Double->double
Double db01=Double.valueOf(12.22);
double db02=db01.doubleValue();
System.out.println(db02);
//7.Boolean->boolean
Boolean bl01=Boolean.valueOf(true);
boolean bl02=bl01.booleanValue();
System.out.println(bl02);
//8.Character->char
Character ch01=Character.valueOf('B');
char ch02=ch01.charValue();
System.out.println(ch02);
}
}
(3)将字符串类型转换成包装类型
public class StringToInt01 {
public static void main(String[] args) {
//将字符串类型转化为包装类型
//1.String->Integer
Integer in01=Integer.valueOf("100");
System.out.println(in01);
//2.String->Double
Double db01=Double.valueOf("12.25");
System.out.println(db01);
//3.String->Float
Float fl01=Float.valueOf("12.25");
System.out.println(fl01);
//4.String->Byte
Byte by01=Byte.valueOf("127");
System.out.println(by01);
//·······
}
}
(4)将字符串转换为基本数据类型
public class StringToInt02 {
public static void main(String[] args) {
//将String字符串转化为基本的数据类型
//1.String->int
int in01=Integer.parseInt("125452");
System.out.println(in01);
//2.String->double
double db01=Double.parseDouble("12.244");
System.out.println(db01);
//3.String->float
float fl01=Float.parseFloat("12.20");
System.out.println(fl01);
//4.String->byte
byte bt01=Byte.parseByte("127");
System.out.println(bt01);
//以此类推····
}
}
(5)自动封箱和自动拆箱【JDK1.5以后】
JDK1.5进行更新后 可以自动完成基本数据类型到对象类型的转换(自动封箱)
对象类型到基本数据类型的转换(自动拆箱)
public class StringToInt03 {
public static void main(String[] args) {
//自动封装箱
//1.
Integer a01=10;
int b01=a01;
//相当于2.
Integer a02=Integer.valueOf(10);
int b02=a02.intValue();
//3.
Double db01=2.5;
double db02=db01;
//相当于4.
Double db03=Double.valueOf(2.5);
double db04=db03.doubleValue();
//5.
Object o01=10;
Object o02=2.35;
//相当于6.
Object o03=Integer.valueOf(10);
Object o04=Double.valueOf(2.35);
}
}