Let’s use Optional to fix our method contract.

Posted on by

Categories:     

100DaysOfProgramming_Day008

A method is a contract; when we define one, we put our thoughts into it. We specify the parameters with their type and also a return type. When we invoke a method, we expect it to behave according to the contract. If it doesn’t, it’s a violation of the contract.

We have been dealing with such a violation all the time. We invoke a method with its proper arguments, and we get a return. However, sometimes we end up getting a null, which is, in fact, a clear violation. We shouldn’t accept such a violation. If a method cannot return the value of the specified type, it should mention that in the method signature, the method may or may not be returning the value you are expecting. If we know it from the method signature, we then write our code accordingly.

Now the question is, how do we define such a contract in a method signature? Well, that’s where Optional comes into play. Set your return type as Optional. Optional is a mystery box, a wrapping paper; it may or may not contain the value. When we specify that in a method signature, we assume that the box might be empty. Let’s see an example-

public static Optional<Book> findBookByName(String name) {
  return books.stream()
          .filter(book -> book.title().equalsIgnoreCase(name))
          .findAny();
}

The method above specified Optional as a return type. It may return the book that I’m looking for or may not. I’m aware of this, and I can deal with it when I invoke it. For example-

    var bookOpt = findBookByName("Java Programming");
    if (bookOpt.isPresent()) {
        var book = bookOpt.get();
        var releasedYear = book.releasedYear();
        System.out.println("Java Programming was published in " + releasedYear);
    } else {
        System.out.println("Book was not found");
    }

Or we can do the same thing with the functional construct, e.g.


findBookByName("Java Programming")
.map(Book::releasedYear)
.ifPresentOrElse((releasedYear) 
        -> System.out.println("Java Programming was published in " + releasedYear),
() -> System.out.println("Book was not found"));

The bottom line is, we should fix our method contract and use optional rather than returning null.

for copy/paste pleasure: https://github.com/rokon12/100DaysOfJava/blob/main/src/main/java/com/bazlur/Day009.java

         

Share on:

Author: A N M Bazlur Rahman

Java enthusiastic | Book author | Mentor | Helping Java Developers to improve their coding & collaboration skills so that they can meet great people & collaborate

100daysofcode 100daysofjava access advance-java agile algorithm arraylist article bangla-book becoming-expert biginteger book calculator checked checked-exceptions cloning code-readability code-review coding coding-convention collection-framework compact-strings completablefuture concatenation concurrency concurrentmodificationexception concurrentskiplistmap counting countingcollections critical-section daemon-thread data-race data-structure datetime day002 deliberate-practice deserialization design-pattern developers duration execute-around executors export fibonacci file file-copy fork/join-common-pool functional future-java-developers groupby hash-function hashmap history history-of-java how-java-performs-better how-java-works http-client image import inspiration io itext-pdf java java-10 java-11 java-17 java-8 java-9 java-developers java-performance java-programming java-thread java-thread-programming java11 java16 java8 lambda-expression learning learning-and-development linkedlist list local-type-inference localdatetime map methodology nio non-blockingio null-pointer-exception object-cloning optional packaging parallel pass-by-reference pass-by-value pdf performance prime-number programming project-loom race-condition readable-code record refactoring review scheduler scrum serialization serversocket simple-calculator socket software-development sorting source-code stack string string-pool stringbuilder swing thread threads tutorial unchecked vector virtual-thread volatile why-java zoneid