How do I sort an ArrayList of objects by each object's integer parameter?

I was A2A. As soon as I started writing my answer I saw answer which is exact replica of what I would have also written. Just to add few more points to the below answer,prefer using comparator instead of comparable.By Using a Comparable you are finalizing the default sorting behaviour for your class which may or may not be useful for others. When to use Comparable: Class should implement the comparable interface when it is the most natural way of sorting objects of that class,and anyone who wants to sort those objects would also do what is done in comparable implementation.Or to be specific use comparable when you want to define default sorting order for objects of a class. When to use Comparator(Prefered Method): When you can't decide upon the natural sorting for your class, then go for this option.As in your case one may want to sort Employee objects either by salary,age,Id etc, so for each of these sorting behaviour use comparator for each sorting criteria. PS:I think you should always refer http://stackoverflow.com/ for all such technical questions.Stack Overflow is a question and answer site for professional and enthusiast programmers containing library of detailed answers to every question about programming.

Many of the classes like String, Integer, Date etc. already  implement comparable interface and for integer natural ordering is ascending so in your case you can use the compareTo method of the comparable interface already implemented by Integer class. Note that it has to be Integer not int. Now you can use either comparator or comparable. I'll suggest you can use Comparable and define the natural ordering for your own class as Employees in ascending order of age.... If you want to sort in any other way  then use a Comparator. Using Comparable -  Your Employee class should implement Comparable and provide implementation for compareTo method. public int compareTo(Employee o) { return this.getAge().compareTo(o.getAge()); } and then in the sorting logic -  Collections.sort(empList); See more here - http://netjs.blogspot.in/2015/08/how-to-sort-arraylist-of-custom-objects-java.html

You can use a comparator and then implement its compareTo method for sorting The return value of the compare method decides the equality of the objects. If return value is a negative number – Object 1 is less than Object 2 If return value is a positive number – Object 1 is greater than Object 2 If return value is 0 – Object 1 is equal to Object 2 You can get more details here http://www.kscodes.com/java/sorting-arraylist-java-using-comparators/