int type (4 bytes) (- 2 ^ 31 ~ 2 ^ 31-1)
In java, one int byte accounts for 4 bytes, which is not directly related to the operating system (8 binary bits = 1 byte)
System.out.println(Integer.MAX_VALUE);//Calculate the maximum and minimum of shaping respectively System.out.println(Integer.MIN_VALUE);
If the result of the operation exceeds the max value of int, an overflow condition occurs.
For the era of big data, data can easily exceed int_max, so the long type is introduced.
long type (8 bytes) (- 2 ^ 64 ~ 2 ^ 64 - 1)
long num=10L; long num1=10l;//Define variables of type long
It is also possible to use 10 for initialization, but it is better to use 10L or 10L.
System.out.println(Long.MAX_VALUE);//Find the maximum and minimum of Long shape respectively System.out.println(Long.MIN_VALUE);
double a = 1.1; System.out.println(a * a);//1.2100000000000002 /*double The layout type complies with IEEE754 standard and tries to use limited memory space to represent koneng's infinite decimal ，There will be some accuracy error*/
Although double in java is also 8 bytes, the memory layout of floating-point numbers is very different from that of integers, and the range cannot be expressed simply in the form of n-power of 2.
float num=1.0f; float num1=1.0F;//initialization
Because float represents a small range of data precision, double is recommended for general floating-point types.
char type (2 bytes)
char ch = 'A';//initialization
In Java, the form of single quotation mark + single letter is used to represent the literal value of a character.
char ch2 = 97;// System.out.println(ch);//The result is a
char in computer is essentially an integer. ASCII is used to represent characters in C language, while Unicode is used to represent characters in Java. Therefore, a character occupies two bytes and represents more types of characters, including Chinese.
Byte (1 byte)
byte value = 0; System.out.println(value); //byte type initialization
Byte types also represent integers.
Byte only takes up one byte, indicating a small range (- 128 - > + 127)
Byte type and character type are irrelevant.
byte ab=10; byte cd=20; byte de=(byte)(ab+cd);//short and byte types are converted to 4-byte int types before calculation, so they need to be cast
short (2 bytes)
short value = 0; System.out.println(value); //short type initialization
The data range represented by short is - 32768 - > + 32767 ps: This indicates that the range is relatively small and is generally not recommended.
boolean (not necessarily)
boolean value = true; System.out.println(value); //boolean type initialization
There are only two values for boolean variables. True means true and false means false
Java boolean type and int cannot be converted to each other. There is no such usage as 1 for true and 0 for false
boolean type. Some JVM s occupy 1 byte and some occupy 1 bit. This is not explicitly specified
String name = "zhangsan"; System.out.println(name);//string type initialization
Java uses double quotation marks + several characters to represent string literals
Unlike the above types, String is not a basic type, but a reference type
Some specific characters in the string that are not convenient for direct representation need to be escaped
Examples of escape characters:
String name = "My name is \"Zhang San\"";
//"\" bit "\" is required for printing bit //"\ \ bit" is required to print \ bit \\“ //Printing \ \ bit \ \ requires "\ \ \ \ bit"\\“
There are many escape characters, some of which are common as follows:
\n line feed
\t horizontal tab
String + operation: Represents string splicing:
String a = "hello"; String b = "world"; String c = a + b; System.out.println(c); //helloworld
You can also splice strings and integers:
String str = "result = "; int a = 10; int b = 20; String result = str + a + b; System.out.println(result); //result=1020
The above code shows that string splicing is performed when there is a string in a + expression Therefore, we can easily use System.out.println to print multiple strings or numbers at the same time:
int a = 10; int b = 20; System.out.println("a = " + a + ",b = " + b);
Introduce the concept of string.valueof()
(1) String.valueOf(boolean b): converts boolean variable B to a string
(2) String.valueOf(char c): converts char variable C to a string
(3) String.valueOf(char data): converts char array data into a string
(4) String.valueOf(char data, int offset, int count): convert count elements from data[offset] in char array data into strings
(5) String.valueOf(double d): converts the double variable d to a string
(6) String.valueOf(float f): converts the float variable f to a string
(7) String.valueOf(int i): converts the int variable I to a string
(8) String.valueOf(long l): converts the long variable l into a string
(9) String.valueOf(Object obj): converts an obj object into a string, which is equal to obj.toString()
Introduce the concept of Integer.parseInt()
Integer.parseInt() converts integer data to basic data type int