This library does not provide anything that you can not achieve with provided java language if else statements. It does not simplify your business logic or if checks, so what it does basically? It helps you to write more readable code and how it does that, let's understand it by examples.

• I saw a similar code snippet in one of projects, It throw exception based on the response code of the response entity

    EmployeeDTO getEmployeeDetail(String employeeCode) {
          ResponseEntity<EmployeeDTO> responseEntity;
          try {
                  responseEntity = restTemplate.getForEntity(url, EmployeeDTO.class);
          } catch(HttpServerErrorException ex) {
              throw EmployeeServiceException("Failed to fetch.......");
          }
  
          if (responseEntity.getStatusCode() != HttpStatus.OK) {
              throw new EmployeeServiceException(format(ERROR_MESSAGE, responseEntity.getStatusCode()));
          }
  
          if (responseEntity.getBody() == null || "".equals(responseEntity.getBody().toString())) {
              throw new NoContentException(format(NO_CONTENT_FOUND_MESSAGE, fromDate, toDate));
          }
  
          return responseEntity.getBody();
    }
  

  Let's write this code with library

    EmployeeDTO getEmployeeDetail(String employeeCode) {
          ResponseEntity<EmployeeDTO> responseEntity;
          try {
               responseEntity = restTemplate.getForEntity(url, EmployeeDTO.class);
          } catch(HttpServerErrorException ex) {
              throw EmployeeServiceException("Failed to fetch.......");
          }
  
      return If.isTrue(responseEntity.getStatusCode() != HttpStatus.OK)
         .thenThrow(() -> new EmployeeServiceException(format(ERROR_MESSAGE, responseEntity.getStatusCode())))
         .elseIf(responseEntity.getBody() == null)
         .thenThrow(() -> new NoContentException(format(NO_CONTENT_FOUND_MESSAGE, fromDate, toDate))
         .elseGet((responseEntity) -> responseEntity.getBody())
    }
  

Don't you think, it is more readable. It tells a better story that you do this otherwise do this or this.

• Let's assume, you have to fetch employee skills provided by multiple services, and based on some flag you fetch the details from one of them and return it. see below

  List getEmployeeSkills(String code) { final EmployeeClient employeeClient; if(isEmployeeGlobalServiceEnabled()) { employeeClient = globalEmployeeServceFactory.getEmployeeClient(); } else { employeeClient = localEmployeeServiceFactory.getEmployeeClient(); } Employee employee = employeeRepository.findByCode(code); return employeeClient.getEmployeeSkills(employee.id) }

Now try to understand the code above, even though very simple statements but you might have spend some time with employeeClient variable to track it. if this method had been large, it would have been more difficult to track it. Every time, we refer a variable, we have to consider all possible assignments to it, if it has multiple assignments we have to understand all of them. Now, let's write the same code using library

List<EmployeeSkill> getEmployeeSkills(String code) {
    final EmployeeClient employeeClient = If.isTrue(isEmployeeGlobalServiceEnabled())
                                            .thenGet(() -> globalEmployeeServceFactory.getEmployeeClient())
                                            .elseGet(() -> localEmployeeServiceFactory.getEmployeeClient())

    Employee employee = employeeRepository.findByCode(code);
    return employeeClient.getEmployeeSkills(employee.id)
}

As a programmerif else are now basic syntax and we don't think, it is an over head for above basic examples because that's what we have been reading since we learnt programming, it takes few extra seconds than normal sequential statements to understand these simple syntax?. But why to spend even seconds on these syntax?

People comes up with argument, what if statements in if else are large block of code. Well, we should take large if else blocks in methods because they are doing one and only one thing and it very cohesive piece of code. How can i say this? because that's the reason they belong together in the block otherwise you would have taken them out of blocks, above or below. You must be thinking, why are we discussion it here? Because this library implicitly(syntax will be difficult) makes you, to refactor large if else code in methods. If you have large block of code, the syntax will make you think about refactoring.

void doSomething() {
   statement0
   If.isTrue(condition)
     .thenCall(() -> {
       statement11
       statement21
       statement31
       statement41
   }).elseCall(() -> {
       statement21
       statement22
       statement23
       statement24
   })
}

then change it to

void doSomething1() {
       statement11
       statement21
       statement31
       statement41
}

void doSomething2() {
       statement21
       statement22
       statement23
       statement24
   }

void doSomething() {
   statement0
   If.isTrue(condition)
     .thenCall(() -> doSomething1())
     .elseCall(() -> doSomething2())
}

1. If else syntax for expression

• If an expression is true then user x otherwise use y

    int allowedSpeed;
    if(currentRoad == "highWay") {
        allowedSpeed = 160km/h;
    } else {
        allowedSpeed = 40km/h;    
    }
  
    setSpeed(allowedSpeed);
  

  Simplified as

    int allowedSpeed = if.isTrue(currentRoad == "highWay")
                         .thenValue(160km/h)
                         .elseValue(40km/h);
    setSpeed(allowedSpeed);
  

  And as

    int allowedSpeed = if.orElse(currentRoad == "highWay", 160km/h, 40km/h);
    setSpeed(allowedSpeed);
  

• If an expression is true then process something otherwise use some other process

    if(currentLocation == "known") {
        driveWithFun();
    } else {
        informPassenger();    
    }
  

  Simplified as

    if.isTrue(currentRoad == "known")
      .thenCall(() -> driveWithFun())
      .elseCall(() -> informPassenger());
  

  And as

    if.orElse(currentRoad == "known", () -> driveWithFun(), () -> informPassenger());
  

• If an expression is true then get a value from one mechanism otherwise from a different one

    int allowedSpeed;
    if(allowedSpeedAtCurrentLocation == "unknown") {
        allowedSpeed = callAFriendAndGetIt();
    } else {
        allowedSpeed = getItFromMyBrain();
    }
  
    accelerateToGivenSpeed(allowedSpeed)
  

  Simplified as

    int allowedSpeed = if.isTrue(allowedSpeedAtCurrentLocation == "unknown")
                         .thenGet(() -> callAFriendAndGetIt())
                         .elseGet(() -> getItFromMyBrain());
    accelerateToGivenSpeed(allowedSpeed)
  

  And as

    int allowedSpeed = if.orElse(allowedSpeedAtCurrentLocation == "unknown",
                                 () -> callAFriendAndGetIt(),
                                 () -> getItFromMyBrain());
  
    accelerateToGivenSpeed(allowedSpeed)
  

• If something unexpected occurred and need to raise exception else process if(currentSpeed == "unacceptable-level") { throw new UnacceptableSpeed(currentSpeed); } else { informSpeedIsAcceptable(); }

    driveSmoothly(allowedSpeed)
  

  Simplified as

    if.isTrue(currentSpeed == "unacceptable-level")
      .thenThrow(() -> new UnacceptableSpeed(currentSpeed))
      .elseCall(() -> informSpeedIsAcceptable());
    driveSmoothly(allowedSpeed)
  

  all the above methods could be used in combinations, please refer test cases for all possible scenarios

2. If else for handling Null object

• when a value is calculated one way, if a variable is null and other way if variable is not null String boxMessage; if(box == null) { boxMessage = "Box does not exist"; } else { boxMessage = "Box exist"; }

    showMessage(boxMessage)
  

  Simplified as

    String boxMessage = if.isNull(box)
                          .thenValue("Box does not exist")
                          .elseValue("Box exist");
    showMessage(boxMessage);
  

  And as

    String boxMessage = if.nullOrElse(box, "Box does not exist", "Box exist");
    showMessage(boxMessage);
  

• A value is calculated if a variable is null otherwise use given value,

    if(boxMessage == null) {
        boxMessage = generateMessage();
    }
  
    showMessage(boxMessage);
  

  Simplified version:

    String boxMessage = if.isNull(boxMessage)
                          .thenGet(() -> generateMessage())
                          .elseValue(boxMessage);
  
    showMessage(boxMessage);
  

• A value is calculated, if a variable is null one way, otherwise use some other way, if(receivedBoxMessage == null) { boxMessage = generateMessage(); } else { boxMessage = generateMessageOtherWay(); }

    showMessage(boxMessage);
  

  Simplified version:

    String boxMessage = if.isNull(receivedBoxMessage)
                          .thenGet(() -> generateMessage())
                          .elseGet(() -> generateMessageOtherWay());
  
    showMessage(boxMessage);
  

  And as:

    String boxMessage = if.isNull(receivedBoxMessage, () -> generateMessage(), () -> generateMessageOtherWay());    
    showMessage(boxMessage);
  

• A value is calculated one way, if a variable is null, otherwise use non null value to generate value, if(receivedBoxMessage == null) { boxMessage = generateMessage(); } else { boxMessage = generateMessage(boxMessage); }

    showMessage(boxMessage);
  

  Simplified version: String boxMessage = if.isNull(receivedBoxMessage) .thenGet(() -> generateMessage()) .elseMap((nonNullReceivedBoxMessage) -> generateMessage(nonNullReceivedBoxMessage));

    showMessage(boxMessage);
  

  And as:

    String boxMessage = if.isNull(receivedBoxMessage,
                                  () -> generateMessage()),
                                  (nonNullReceivedBoxMessage) -> generateMessage(nonNullReceivedBoxMessage));
  
    showMessage(boxMessage);
  

• If you would like to throw an exception, if a value is null, otherwise proceed,

    if(boxMessage == null) {
        throw new NotFoundException("Message not found");
    } else {
        boxMessage = generateMessage(boxMessage);
    }
  
    showMessage(boxMessage)
  

  Simplified version:

    String boxMessage = if.isNull(receivedBoxMessage)
                          .thenThrow(new NotFoundException("Message not found"))
                          .elseMap((nonNullReceivedBoxMessage) -> generateMessage(nonNullReceivedBoxMessage));
  
    showMessage(boxMessage)
  

and so on. see test cases to know more about available options.

3. do something only if some condition is true, else part is empty

• If you like to process something when condition is true else nothing

    if(purseStatus == "not found) {
        putCashInPocket(cash);
    }
    goToShopping();
  

  Simplified version:

    if.isTrueThen(purseStatus == "not found").thenCall(() -> putCashInPocket(cash))
    goToShopping();
  

  And as:

    if.isTrueThen(purseStatus == "not found", () -> putCashInPocket(cash))
    goToShopping();
  

• If you throw some exception when condition is met otherwise perform operations normally

    if(breakStatus == "not working") {
        throw new BreakNotWorking();
    }
    keepDriving();
  

  Simplified version:

    if.isTrueThen(breakStatus == "not working")).thenThrow(() -> new BreakNotWorking())
    keepDriving();