In Java, the member variables of a class define the attributes of the class. For example, a student class generally needs to have attributes such as name, gender, and age. In this case, it is necessary to define three attributes: name, gender, and age.
Recommended course: Java Tutorial.
The syntax for declaring member variables is as follows:
[public|protected|private][static][final]<type><variable_name>
The meaning of each parameter is as follows.
public, protected, private: used to indicate the access rights of member variables.
static: Indicates that the member variable is a class variable, also called a static variable.
final: Indicates that the member variable is declared as a constant and its value cannot be changed.
type: Indicates the type of the variable. variable_name: Indicates the variable name.
You can initialize a member variable while declaring it. If the member variable is not initialized when declaring it, the system will initialize the member variable with a default value.
The default value of initialization is as follows:
The default value of basic type variables of integer type (byte, short, int and long) is 0.
The default value of the basic type variable of single-precision floating point type (float) is 0.0f.
The default value of the basic type variable of double precision floating point type (double) is 0.0d.
The default value of the basic type variable of character type (char) is "\u0000".
The default value of Boolean basic type variables is false.
The default value of a variable of array reference type is null.
If you create an instance of an array variable but do not explicitly assign a value to each element, the initialization value of the elements in the array adopts the default value corresponding to the array data type.
An example of defining attributes of a class is as follows:
public class Student
{
public String name; //姓名
final int sex=0; //性别：0表示女孩，1表示男孩
private int age; //年龄
}
The Student class in the above example defines three member variables: name of String type, sex of int type and age of int type.
Among them, the access modifier of
name is public, and the initialization value is null; the access modifier of
sex is friendly (default), and the initialization value is 0, indicating that the gender is female, and its value cannot be changed; the access modifier of
age is private, and the initialization value is 0.
Example:
public class Counter
{
static int sum;
public static void main(String[] args)
{
System.out.println(sum);
}
}
Use a static method to modify the variable sum, and the output result is the initial value of the int type, that is: 0.
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