How to create java class attributes

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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