title: 'Interface comparable'

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The compareTo method required by the Comparable interface gets as its parameter the object to which the "this" object is compared. If the "this" object comes before the object received as a parameter in terms of sorting order, the method should return a negative number. If, on the other hand, id "this" object comes after the object received as a parameter, the method should return a positive number. Otherwise, 0 is returned. The sorting resulting from the `compareTo` method is called *natural ordering*.

Let's take a look at this with the help of a Member class that represents a child or youth who belongs to a club. Each club member has a name and height. The club members shoudl go to eat in order of height, so the Member class should implement the `Comparable` interface. The Comparable interface takes as its type parameter the class that is the subject of the comparison. We'll use the same `Member` class as the type parameter.

Since returning a negative number from the `compareTo ()` is enough if the `this` object is smaller than the parameter object, and zero when the lengths are the same, the `compareTo` method described above can also be implemented as follows.

Since the Member class implements the Comparable interface, it is possible to sort the list by using the `sorted` method. In fact, objects of any class that implements the `Comparable` interface can be sorted using the `sorted` method. Be aware, however, that a stream does not sort the original list - *only the items in the stream are sorted*.

If a programmer wants to organize the original list, the `sort` method of the` Collections` class should be used. This of course assumes that the objects on the list implement the `Comparable` interface.

You are provided with the class human. A human has a name and wage information. Implement the interface `Comparable` in a way, that the overridden `compareTo`-method sorts the humans according to wage from biggest to smallest salary.

The exercise template includes the class Student, which has a name. Implement the `Comprable`-interface in the Student-class in a way, that the `compareTo`-method sorts the students in alphabetical order based on their names.

**Hint:** The name of the Student is a String, which implements `Comparable` itself. You may use it's `compareTo`-method for your advantage when implementing the method for the `Student`-class. Note that `String.compareTo` also treats letters according to their size, while the `compareToIgnoreCase`-method of the same class ignores the capitalization completely. You may either of these methods in the exercise.

A class can implement multiple interfaces. Multiple interfaces are implemented by separating the implemented interfaces with commas (`public class ... implements *FirstInterface*, * SecondInterface * ...`). Implementing multiple interfaces requires us to implement all the of the methods whose implementations are required by the interfaces.

<p>Both the `sort` method of `Collections` class and the stream's `sorted` method accept a lambda expression as a parameter that defines the sorting criteria. More specifically, both methods can be provided with an object that implements the <a href="https://docs.oracle.com/javase/8/docs/api/java/util/Comparator.html" target="_blank"> Comparator </a> interface, which defines the desired order - the lambda expression is used to create this object.</p>

String[] pieces = mjono.split(",");

<p>We sometimes want to sort items based on a number of things. Let's look at an example in which films are listed in order of their name and year of release. We'll make use of Java's <a href="https://docs.oracle.com/javase/8/docs/api/java/util/Comparator.html" target="_blank" norel>Comparator</a> class here, which offers us the functionality required for sorting. Le'ts assume that we have the clas `Film` at our disposal.</p>

When we sort objects, the `comparing` and` thenComparing` methods are given a reference to the object's type - the method is called in order and the values ​​returned by the method are compared. The method reference is given as `Class::method`. In the example below, we print movies by year and title in order.

The program asks for new books until the user gives an empty String (only presses enter). After this, the program will print the amount- and names of the books.