Doubt About CompareTo method() ?

[makpandian]

Dear All,

class Man 
implements Comparable<Man>
{
	
	String name;
	int age;
	
	public Man(String name,int age) {
		
		this.age=age;
		
		this.name=name;
		
	}
}

This is my Man class . I have to implement the comparable interface in my Man class for sorting .I have to check both age and name in my compareTo method. For Ex if two man are same age , I have to sort depend on the name.

How can we do this ?

public int compareTo(Man obj) {
		
		if(age > obj.age ) return 1;
		
		else if(age < obj.age ) return -1;
		
		else return name.compareTo(obj.name);
		
		
	}

The preceding code is my try. I am not sure whether it is right or not.

[Petr]

Yeah You wrote a correct code. What are you not sure? You can find more information in API String#compareTo

[makpandian]

Thanks Dude.

What if I have to compare depend on age and grade!

Is this right code.

public int compareTo(Man obj) {

if(age > obj.age ) return 1;

else if(age < obj.age ) return -1;

else {

if(grade> obj.grade) return 1;

else if(grade< obj.grade) return -1;

else return 0;

}

}

[Tolls]

Can't you write a simple test to see if it works?
Wouldn't that be quicker than posting here and waiting for an answer?

[makpandian]

Tolls,

I can , I did so. It s working fine. Is this a good way to implement comparable interface?

[pbrockway2]

For things like ints, consider replacing the two if statements with a subtraction.

[makpandian]

Thanks pbrockway2.

I think if we do subtraction for ints we could not get the rigt result, could't we ?

If possible can u please post ur sample code here?

[DarrylBurke]

if(age == obj.age) {
  return grade - obj.grade;
} else {
  return age - obj.age;
}

Note that the contract of Comparable requires the return value to be positive, negative or zero -- not necessarily +1 / -1 / 0.

db

[pbrockway2]

I think if we do subtraction for ints we could not get the rigt result, could't we ?

The best way to see if to try it by writing a simple by-age comparator for your Man class. (compareTo() being a one line method!). I think it's perfectly possible for such a comparator to sucessfully sort some same data by age. If you think not, post your code illustrating this.