Question

Where can I use an instance method and where is it appropriate to use a class method?

I know the term of class and instance method.

Answer 1

Static methods are class level methods, they are good for utility methods for example Math class in Java. These classes usually take a few inputs work with them and gives desired output(For example Math.pow(4,5)).

Instance methods rather work with the whole object in question. Good example would be almost any class of Java. Still, for example; FileInputStream where read() method reads data from underlying stream.

Example of static method would be

class Math(){
public static long multiply(long a, long b){
   return a*b;
}
public static void main(String[]args){
  System.out.println(Math.multiply());
}
}

Example of instance method can be

class User(){
private String pass;
private String uname;

    public User(String p,String u){
      pass=p;
      uname=u;
    }
    public boolean authenticate(){
      if("secret".equals(this.pass) && "Grrrr".equals(this.uname){
         return true;
      }else{
         return false;
      }
    }
    public static void main(String[]args){
     User u = new User("wrong secret","grrr");
     System.out.println(u.authenticate());
    }
  }

In the second example pay attention to the fact that to use the instance method we must create an object first and then only call the method.