Hello everyone, small music again, Previous: Le Java byte data type of the two variables: Java constants and variables,
Today, Java variables and then say three types of data: data types with the escape character
A data type
1. Definitions
Java is a strongly typed language, data are provided for each corresponding data type.
Java data types
2, classification
A: Basic Data Type: eight kinds of class 4
B: reference data types: class, interface, array.
3, the basic data types
① integer number of bits occupying byte / bit range
byte (byte) 18 bits [-128, 127]
short (short integer) 2 16 [-32768, 32767]
int (integer) 4 32 [-21 million 2100000000]
long (long integer) 8. 64 very big
Note: The default value of an integer type int, long if you need to define a variable of type int when out of range, the need to increase the value l or when L
② float
float (single-precision) 4
double (double precision) 8
Bit 7 is effectively float, double significant bit is 14
Note: The default type double floating point, if you need to define a variable of type float, the value f or the need to add F
③ character (0 to 65535)
char (character) a character can store 2 a Chinese characters
Requirements: The '' character enclosed
④ Logical (Boolean)
boolean (Boolean) 1
4, note:
The default integer type is int, float Default is double.
To add long integers L or l, single-precision floating-point add to F or f.
Second, the data type conversion
1. Definitions
boolean type does not participate in the conversion
2, the default conversion
A: small to large
B:byte,short,char --> int long float double
C: between byte, short, char is the same level, not interchangeable, transferred directly involved in computing an int.
3, cast
A: descending
B: There may be loss of accuracy is generally not recommended for such use.
C: format:
The target variable name = data type (data type target) (converted data);
4 Questions and interview questions:
A: Is there a difference two ways?
float f1 = 12.345f;
float f2 = (float) 12.345; downcasting, the default floating-point type double
B: The following program has a problem, and if so, where is it?
byte b1 = 3;
byte b2 = 4;
byte b3 = b1 + b2;
short s1=3;
short s2=3;
short s3=s1+s2;
char c1=3;
char c2=4;
char c3=c1+c2;
byte, short, char during operation, automatically upcast int type, the returned result is int type, int type received are not, because the type does not match, the error
byte b4 = 3 + 4;
short s=3+4;
Value is calculated constant, when the pre-compiler can determine whether it is out of range
int a=1;
int b=2;
int c=a+b;
long l1=3l;
long l2=3l;
long l3=l1+l2;
float f1=2.3f;
float f2=2.3f;
float f3=f1+f2;
double d1=3.7;
double d2=3.9;
double d3=d1+d2;
Are not being given, java optimized.
C: What is it the result of the following actions?
byte b = (byte)130;
D: characters involved in computing
It is to look inside the ASCII value
'a' 97
'A' 65
'0' 48
Space 32
System.out.println('a');
System.out.println('a' + 1);
E: String involved in computing
In fact, here is the connection string
System.out.println("hello"+'a'+1);
System.out.println('a'+1+"hello");
System.out.println("5+5="+5+5);
System.out.println(5+5+"=5+5");
Operating results: helloa1
98hello
5+5=55
10=5+5
Third, the escape character
\ ': Represents a single quote
\\: Represents a backslash character "\"
\ ": Represents a double quote character
\ B: backspace, is to move the cursor to a character before the current character, it does not delete the current character.
Note: eclipse which does not recognize the need to run in a DOS environment
\ N: line feed, the current position to the beginning of the next line
Enter the beginning, the current position to move to the Bank: \ r
Note: \ n, \ r no difference in eclipse, you need to run in a DOS environment
\ T: Horizontal tab position: Tab jumps to the next position