1, variable
- Where to computing operation (processing) of data is variable, used to store data and calculations to participate in operations.
- Variables are identified by the variable name.
- Variable names consist of alphanumeric and underscores, not beginning with a digit.
【正确】number，number1，number_1，_number
[Error] 1number, 1_number
- Variable must first declare its data type can be used, such as a person ages will explain it is an integer, a person's birthday, we should state that it is a date.
[Format] data type variable name; // variable data type introduced in the next lesson
[Example] Integer age; // declares an integer variable
[Example] Date birthday; // declare a variable date
- Initialization variable assignment, the variable is not assigned and initialized, the initial variable is null.
[Initialization] Integer a = 1, b, c; // variable a value assigned to a variable, while variables declared
[Assignment]
Integer a = 1, b, c; // b, c declared when there is no specified value
b = 1; // specified value in use
c = a + b; // specified value in use
- You must have a value when the variable participate in operations.
[Example 1] + 1 = 2 is calculated
【correct】
Integer a=1,b=1,c;
c=a+b;
[Error ]
Integer a=1,b,c;
c=a+b;
【error】
Integer a=1,b=1;
c=a+b;
- Variables are not case sensitive.
【error】
A Integer; Double A; // A variable declared, can not be repeated statement
2, Constant
- Once a variable declaration or assignment will not change their values.
- Use the keyword final when constant declaration.
- When throughout the program variables you should have a constant value, constant use.
【correct】
final Double PI=3.14 ;
【error】
final Double PI=3.14 ;
PI=PI+1;
3, an example of
(1) 5 + 6, and seek
(2) the known radius 10, of circular perimeter and area
