The Java Code Review Checklist

A code review guide and checklist when working with Java and related technologies. The following should really help when writing new code in Java applications after upgrading to Java 8 or refactoring code that is < Java8

Core Java

Prefer Lambdas

Instead of

Runnable runner = new Runnable(){
    public void run(){
        System.out.println("I am running");
    }
};

do...

Runnable running = () -> {
    System.out.println("I am running");
};

Refactor interfaces with default methods

Instead of

public class MyClass implements InterfaceA {
 
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
    }
 
    @Override
    public void saySomething() {
        System.out.println("Hello World");
    }
 
}
 
interface InterfaceA {
  public void saySomething(); 
 
}

Use default methods. Make sure you do not do this as a a habit because this pattern pollutes interfaces.

public class MyClass implements InterfaceA {
 
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
    }
 
    @Override
    public void saySomething() {
        System.out.println("Hello World");
    }
 
}
 
interface InterfaceA {
 
    public void saySomething();
 
    default public void sayHi() {
      System.out.println("Hi");
    }
 
}

Prefer Streams to reduce code.

private static void printNames(List persons, Predicate predicate) {
            persons.stream()
                    .filter(predicate)
                    .map(p -> p.getName())
                    .forEach(name -> System.out.println(name));
        }
}

Use Parallel sorting

Instead of

Array.sort(myArray);

Use...

Arrays.parallelSort(myArray);

Depend on parameter reflection

Instead of...

Person getEmployee(@PathParam("dept") Long dept, @QueryParam("id") Long id)

Do...

Person getEmployee(@PathParam Long dept, @QueryParam Long id)

Since params names as same as var names.

Prefer to use "filter / map / reduce" approach

List<String> names = Arrays.asList("Smith", "Adams", "Crawford"); 
List<Person> people = peopleDAO.find("London"); 
  
// Using anyMatch and method reference 
List<Person> anyMatch = people.stream().filter(p -> (names.stream().anyMatch(p.name::contains))).collect(Collectors.toList()); 
  
// Using reduce 
List<Person> reduced = people.stream().filter(p -> names.stream().reduce(false (Boolean b, String keyword) -> b || p.name.contains(keyword), (l, r) -> l | r)).collect(Collectors.toList()); 

Use new data-time api

Clock clock = Clock.systemUTC(); //return the current time based on your system clock and set to UTC. 

Clock clock = Clock.systemDefaultZone(); //return time based on system clock zone 

long time = clock.millis(); //time in milliseconds from January 1st, 1970