problem with your code you are creating multiple Model objects try this code
public StaffInformation(){
ModelClass mc = new ModelClass();
mc.setName("Khan");
mc.setAge(30);
mc.setAddress("NY");
Main.displayData(mc);
}
Here is your main class
class Main{
public static displayData(ModelClass mc)
{
System.out.println(mc.getAge());
System.out.println(mc.getName());
System.out.println(mc.getAddress());
}
public static void main(String[] args) {
StaffInformation sc=new StaffInformation();
}
}