CS118 cramming cheat sheet

What happens when we have an else/else if without curly braces?

• Dangling else problem

• else will default to the last if that came before it

  • Code may not execute if else was meant for the first if in the block, and several if’s came after it

What is the issue of going from long → int and how can it be overcome?

• long is more precise than int

• Could lead to a lossy conversion where data is lost and might be less precise

• Requires a change in return type or an explicit cast

Where can’t switch statements be used?

• Where there are no discrete values present (e.g. case is an inequality or a range)

What is the process of dealing with a Q2/3-type programming problem?

• Understand the prompt — identify nouns and verbs, and what concept they relate to

• Split the task into several steps, input → output → calculation

• Simplify using variables and arrows

• Think about how they can be implemented in Java

How should we deal with fields implementing data structures in classes?

• Declare the field in the class

• Do not pass it in as a parameter in the constructor, but initialise it within the constructor block

class ClassName { 
 	List<E> list
	int p1;
	int p2;
	
	public ClassName(int p1, int p2) {
		this.p1 = p1;
		this.p2 = p2;
		this.list = new ArrayList<>();
	}
	// ...
}

How should abstract classes and methods be implemented?

• Declare the method as abstract but do not implement it

• Inside concrete class, implement the method using @Override notation (without calling it abstract)

How should checked and unchecked exception classes be handled?

• Unchecked → exception is a subclass of RuntimeException

• Checked → exception is a subclass of Exception

How should exception-throwing methods be declared?

public [ReturnType] method throws [ExceptionName](…) { … }

throws MUST be there if the method is throwing the exception

What is the format of a generic class?

• Uses <T> to show that it is a generic class

class ClassName<T> { … }

What would the generic class look like if the generic type can only be subclasses of another type?

Using List<?> as an example:

class ClassName<T extends List<?>> { … }

How are interfaces implemented?

• Interface only stores the method signature (no body)

• @Override notation when we implement the methods defined in the interface

• Included in the class:

public class [ClassName] implements [InterfaceName] { … }

When is @Override notation used?

• Either when we implement a method from an interface, or we are overriding a method from a superclass