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Java Class Attributes
Java Class Attributes
In the previous chapter, we used the word "variable" in x in the example (as shown below). It is actually a attribute of the class. Or do not say that the characteristics of the class vary within the classroom:
Example
Create a class called "Main" with two attributes: x and y:
public class Main {
int x = 5;
int y = 3;
}
Another name for class attributes fields.
Accessing Attributes
You can access attributes by creating a class object, and using the dot syntax (.):
The following example will create a Main class object, with the name myObj. We use the x attribute on an object to print its value:
Example
Create an object called "myObj" and print the value of x:
public class Main {
int x = 5;
public static void main(String[] args) {
Main myObj = new Main();
System.out.println(myObj.x);
}
}
Modify Attributes
You can also adjust attribute values:
Example
Set the value of x to 40:
public class Main {
int x;
public static void main(String[] args) {
Main myObj = new Main();
myObj.x = 40;
System.out.println(myObj.x);
}
}
Or subtract existing prices:
Example
Change the value of x to 25:
public class Main {
int x = 10;
public static void main(String[] args) {
Main myObj = new Main();
myObj.x = 25; // x is now 25
System.out.println(myObj.x);
}
}
If you do not want the ability to override existing values, declare the attribute as the final:
Example
public class Main {
final int x = 10;
public static void main(String[] args) {
Main myObj = new Main();
myObj.x = 25; // will generate an error: cannot assign a value to a final variable
System.out.println(myObj.x);
}
}
The final keyword is useful if you want the variable to always keep the same value, such as PI (3.14159 ...).
The final keyword is called "modifier".
Multiple Objects
If you create multiple objects in one category, you can change attribute values in one item, without affecting attribute values in another:
Example
Change the value of x to 25 in myObj2, and leave x in myObj1 unchanged:
public class Main {
int x = 5;
public static void main(String[] args) {
Main myObj1 = new Main(); // Object 1
Main myObj2 = new Main(); // Object 2
myObj2.x = 25;
System.out.println(myObj1.x); // Outputs 5
System.out.println(myObj2.x); // Outputs 25
}
}
Multiple Attributes
You can specify as many attributes as you want:
Example
public class Main {
String fname = "John";
String lname = "Doe";
int age = 24;
public static void main(String[] args) {
Main myObj = new Main();
System.out.println("Name: " + myObj.fname + " " + myObj.lname);
System.out.println("Age: " + myObj.age);
}
}