A class variable is any field declared with the static modifier; this tells the compiler that there is exactly one copy of this variable in existence, regardless of how many times the class has been instantiated.
Java Class Variable Example
Consider these are 100 students in a college named "ABC", each student have their own unique roll number and name but the college remains the same among all the 100 students. The college field is declared as static so it can occupy memory only once.
package net.javaguides.corejava.variables;
public class StaticVariableExample {
public static void main(String[] args) {
Student student = new Student(100, "Student 1");
Student student2 = new Student(101, "Student 2");
Student student3 = new Student(102, "Student 3");
Student student4 = new Student(103, "Student 4");
System.out.println(" ------------ Student 1 -------------");
System.out.println(student.toString());
System.out.println(student2.toString());
System.out.println(student3.toString());
System.out.println(student4.toString());
}
}
class Student {
private int rollNo;
private String name;
private static String college = "ABC"; // static variable
public Student(int rollNo, String name) {
super();
this.rollNo = rollNo;
this.name = name;
}
@Override
public String toString() {
return "Student [rollNo=" + rollNo + ", name=" + name + ", college=" + college + "]";
}
}
Output:
Student [rollNo=100, name=Student 1, college=ABC]
Student [rollNo=101, name=Student 2, college=ABC]
Student [rollNo=102, name=Student 3, college=ABC]
Student [rollNo=103, name=Student 4, college=ABC]
Note that, all the students have the same college "ABC".
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