Hygiene Guide - Data Types

7. Data Types

7.1 Type parameters (generics)

Always include the type parameter when dealing with generic classes such as ArrayList, TreeSet, etc. Failing to do so will likely lead to casting that clutter up the code and/or unsafe type operations.

Bad

			Stack visited = new Stack();
		

Good

			Stack<String> visited = new Stack<>();

		

7. 2 Casting

Avoid casting of object types. Casting to object types is essentially disregarding the safety net of the type system that Java provides. It may achieve the desired behavior, but it is usually a sign that we should change the logic of our program elsewhere. Casting to object types should only be done if truly necessary, typically in an equals method and sometimes in order to write a more efficient version of an algorithm.

Casting to primitive types to actually convert values is fine, however, e.g.

		int truncated = (int) (Math.random() * 5);
		The place you will most likely cast objects is when overriding the 
		equals method. We do not want to overload equals so the parameter shall 
		be of type Object. Use instanceof operator 
		or the getClass() method, to check the 
		parameter is the same type as the this 
		object before casting.

		If the class uses generic types, do not attempt to cast to the 
		generic type parameter. Use the wildcard or Object as the data type of 
		the elements of the target of the cast.

		Example:

		public class GenericList<E> {

    private E[] container;

    public boolean equals(Object obj) { // NOT GenericList<E> obj 
		or GenericList obj. That overloads equals

        if (obj instanceof GenericList<?>) { 
		// obj instanceof GenericList<E> is a syntax error

            GenericList<?> 
		otherList = (GenericList<?>) obj;

            // 
		GenericList<E> otherList = (GenericList<E>) obj is NOT SAFE and not 
		allowed in 314.

7.3 Prefer simple data types

Sometimes we have options for how we want to represent the data and either option(s) will be able to produce correct behavior. Instead of using a more complicated representation that can do everything we want and more, we should try use the representation that fits the specific problem the best. The intent and logic of your code will be simpler to another reader. Some examples are listed below.

If you’re using an int to keep track of whether it’s one value or another with only 2 choices, use a boolean instead.
If you’re using a String to keep track of a single letter, use a char.
Do not use boxed types unless you need them to store in a generic data structure. If you’re using Integer because you want to keep track of a sum, just use int. Likewise for Character and char AND Double and double.

The point of a data structure is to store related values. If a data structure is only used to store one or two values, we prefer to use those value(s) directly.