How to Sort Java Collections: Comparator, Comparable, and Lambda Expressions?

Sorting Java Collections

To sort a Java Collection, there are several approaches to consider, depending on the specific requirements. One common option is to utilize a Comparator.

Using a Comparator:

Create a Comparator class that implements the Comparator interface. Within the compare() method, you define the logic for comparing objects. For example, to sort a CustomObject by its id field:

Comparator<CustomObject> comparator = new Comparator<CustomObject>() {
    @Override
    public int compare(CustomObject left, CustomObject right) {
        return left.getId() - right.getId();
    }
};

Then, use the Comparator to sort the collection using Collections.sort():

Collections.sort(list, comparator);

Alternatively, if your CustomObject implements Comparable, you can directly use Collections.sort(list).

With JDK 8 Lambda Expressions:

Introduced in JDK 8, lambda expressions provide a convenient way to write Comparators:

Collections.sort(list, (left, right) -> left.getId() - right.getId());

Shorthand Notation with JDK 8:

For simple scenarios, the following shorthand notation can be used to sort by a specific field:

list.sort(Comparator.comparing(CustomObject::getId));

Ultimately, the best approach for sorting a Java Collection depends on the specific needs and Java version being used.

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