I can use it to sort by emp id but I'm not sure if it is possible to compare strings. I get an error the operator is undefined for strings.
public int compareTo(Emp i) {
if (this.getName() == ((Emp ) i).getName())
return 0;
else if ((this.getName()) > ((Emp ) i).getName())
return 1;
else
return -1;
What you need to use is the compareTo()
method of Strings.
return this.getName().compareTo(i.getName());
That should do what you want.
Usually when implementing the Comparable
interface, you will just aggregate the results of using other Comparable
members of the class.
Below is a pretty typical implementation of a compareTo()
method:
class Car implements Comparable<Car> {
int year;
String make, model;
public int compareTo(Car other) {
if (!this.make.equalsIgnoreCase(other.make))
return this.make.compareTo(other.make);
if (!this.model.equalsIgnoreCase(other.model))
return this.model.compareTo(other.model);
return this.year - other.year;
}
}
Pretty sure your code can just be written like this:
public int compareTo(Emp other)
{
return this.getName().compareTo(other.getName());
}
Java String already implements Comparable. So you could simply write your method as
public int compareTo(Emp emp) {
return this.getName().compareTo(emp.getName());
}
(ofcourse make sure you add proper validations such as null checks etc)
Also in your code, do not try to compare Strings using '=='. Use 'equals' method instead. '==' only compare string references while equals semantically compares two strings.
You don't need to cast i to Emp, it's already an Emp:
public int compareTo(Emp i) {
return getName().compareTo(i.getName());
}
Shouldn't
if (this.getName() == ((Emp ) i).getName())
be
if (this.getName().equals(i.getName()))