Question

Class Alkio of my previous! question is chosen to do more methods.
Implement to the class in addition to the previous ones following
methods:

public boolean suurempiArvo(Alkio verrattava)

and

public int compareTo(Alkio verrattava)

Method suurempiArvo returns true, if the value of the object is
greater than value of verrattava. Method compareTo compares the
values of elements and returns an integer( negative, if the value of
the object is less that value of verrattava, zero, is values are the
same and otherwise positive)

Questions.

Why those methods which are used has just one parameter although methods require values of two elements? If I refer in the methods to verrattava by writing verrattava, how do I refer to object?

Answer 1

When you have a method

public int compareTo(SomeObject other) {
    // needs implementation
}

You are comparing other with the current instance. That is to say, the reason why you do not need the second element in the signature is that the second element is already there, it’s the object whose method is being invoked. You compare the members of other with the members of the present instance, basically this, in order to arrive at the proper result.

public int compareTo(SomeObject other) {
    // assumes member variable foo
    if (this.foo > other.foo) {
        // you finish implementation 
    } 
}

For clarification, if you were to invoke these methods, it would be something like

SomeObject first = new SomeObject();
SomeObject second = new SomeObject();
int result = first.compareTo(second); 

So you pass the second object into the compareTo method of first. first then compares itself against the second (this vs. other).