类型转换

自动类型转换

byte,short,char->int->long->float->double

byte,short,char三者之间不相互转换,再运算的时候,都把自己提升为int去操作

int 转 long

int i = 6;

long l = i;

long 转 float

long l = 6;

float f = l;

float 转 double

float f = 6;

double d = f;

强制类型转换

double->flost->long->int

把范围大的数据类型,强制转换为范围小的数据类型
注:会损失精度

int 转 byte

int a = 2;
byte b = 3;

//(a+b):在括号中先运算 
//(byte): 指运算后要转换后的类型
int c = (byte)(a + b);

类型相互转换

Byte 转 String

Byte b = 6;
String s = String.valueOf(b);

int转Integer

int i = 10;
Integer integer = new Integer(i);

int转String

int i = 10;

//第一种
String s =String.valueOf(i);

//第二种
String s =Ingeger.toString(i);

//第三种
String s = "" +i;

Long 转 String

Long l = 8L;
String s = String.valueOf(l);

Double 转 String

Double dou = 1.9;
String s = String.valueOf(d);

Integer 转 int

Integer integer = new Integer(10);

int k = integer.intValue();

Integer 转 String

Integer integer = new Integer(10);

//第一种
String str = integer.toString();

//第二种
String str = integer + "";

//第三种
String.valueOf(integer);

String 转 Byte

String str = "6";

//第一种
byte b = Byte.parseByte(str);

//第二种
Byte b = Byte.valueOf(str);

String 转 int

String str ="10"; 

//先把string转成Integer
Integer integer = newInterger(str); 

//再把Integer转成int
int i = integer.intValue(); 

String 转 Integer

String str = "10";

//第一种
Integer integer =Integer.valueOf(str);

//第二种
Integer integer = Integer.parseInt(str);

String 转 Double

String str = "2.9";
Double d = Double.valueOf(str);

String 转 Long

String str = "6";

//第一种
Long l = Long.valueOf(str);

//第二种
long l = Long.parseLong(str);

String 转 BigDecimal

String str = "10";

BigDecimal bigDecimal = new BigDecimal(str);

String 转 Date

String string = "2020-08-30";
DateFormat format = new SimpleDateFormat("yyyy-MM-dd");
Date parse = format.parse(string);

String日期 转 Timestamp

String s = "9999-12-30 00:00:00";
Timestamp timestamp = Timestamp.valueOf(s);

BigDecimal 转 String

BigDecimal bigDecimal = new BigDecimal("1000000");
String string = bigDecimal.toString();

Date 转 String

Date date = new Date();
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");
String format = simpleDateFormat.format(date);

Date 转 Timestamp

Timestamp timestamp = new Timestamp(date.getTime());

Timestamp 转 String

Timestamp timestamp = new Timestamp(System.currentTimeMillis());

//第一种
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
String format = simpleDateFormat.format(timestamp);

//第二种
String string = timestamp.toString();

Timestamp 转 Date

Timestamp timestamp = new Timestamp(System.currentTimeMillis());
Date date = new Date();
date = timestamp;