Section 1
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If a parent class has no zero-argument constructor, what is the NAME of the first method the child must call?
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Cards (71)
Section 1
(50 cards)
If a parent class has no zero-argument constructor, what is the NAME of the first method the child must call?
super()
If a parent class has an abstract method, what does this mean for the child?
A class derived from the abstract class must implement all those methods that are declared as abstract in the parent class. If a child does not implement all the abstract methods of abstract parent class, then the child class must need to be declared abstract as well.
What interface does an object need to implement to be used in a TreeSet?
All elements inserted into the TreeSet must implement the Comparable interface.
Which data structure you should choose if you want to store data that will be accessed with their index?
Array or ArrayList. Not HashMap or LinkedList
Subclasses can access protected instance variables from the parent class
True
Write a function that takes in a List of Integers and returns the sum:
A private instance variable must have both a getter and a setter.
False
A class has to have a constructor.
Java provides a default parameterless constructor. Ok with the answer being either True or False as long as that is the explanation.
A class can have a private constructor.
True
Write a method that copies all elements of an ArrayList of String into an array of Strings.
We always implement an abstract class and extend an interface.
False. We always extend an abstract class and implement an interface.
Which data structure should you choose if you want to remove existing data.
HashMap or LinkedList Not Array and ArrayList
A child class has to implement any abstract methods declared in the parent class.
True
An abstract class can extend another abstract class.
True
We can call a method in a class if:
We're inside the class; we instantiate the object and the method is public; the method is static
Can an interface have abstract methods?
Yes
Does a class with an abstract method need to be declared as abstract?
Yes
A class has been declared by saying public class Exam{ // there is some stuff here } Inside this class the word super cannot be used since it does not extend any class.
False
It is possible to have the two methods public String make(String s) and public int make(String s) in the same class.
False
A Finally block will get invoke whether the exception is thrown or not
True
Arrays in Java are dynamically sized.
False
What is the default implementation of the equals(Object o) method?
The equals method for class Object implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference values x and y, this method returns true if and only if x and y refer to the same object (x == y has the value true)(dress equivalence of the obj).
Can we store doubles in an array that is declared as integers?
No
An abstract class can implement an interface.
True.
You already have Student class. Declare a hashmap that can map studentkeys to Student objects.
HashMap<String, Student> mapping; or HashMap<String, Student> mapping = new HashMap<String, Student>();
Can we store integers in an array that is declared as doubles
Yes but you can't go the other way
int a = (int)"4" can this compile?
No
An abstract class will always have an abstract method.
False. A class can be made abstract just to make sure that you never create an instance of the class itself but only of subclasses.
What does the word collision mean with respect to hashing?
When we put objects into a hashtable, it is possible that different objects (by the equals() method) might have the same hashcode. This is called a collision.
A class can implement 3 interfaces.
True
Every class needs a main method.
False
Declare an integer array that can hold 100 numbers.
int[] arr = new int[100];
A catch block can exist without a try block.
False
Write a function that takes in a String and returns its reverse. (Hint: use the charAt(int index) function)
What is an example of a static method other than the ones in the Math class that Java provides to you?
Integer.parseInt Math.abs or Math.sqrt don't count Integer.compare Double.Max_Value Double.toString
Can an interface have non-abstract methods?
No
A class must have a constructor.
True
What can be stored in a single Java array?
Primitive types; strings; objects; but it can only do one type it can't do two types ex. ints and doubles not allowed
What is the significance of the @Before tag in a JUnit Test?
The code marked @Before will be executed before each test. This is useful for writing many tests that need similar objects or need to run similar code before they run. accepted The code marked @Before is executed before each test, while @BeforeClass runs once before the entire test fixture. If your test class has ten tests, @Before code will be executed ten times, but @BeforeClass will be executed only once. If you only need setup once, you use @BeforeClass when multiple tests need to share the same computationally expensive setup code. You can move code from @BeforeClass into @Before, but your test run may take longer. Note that the code marked @BeforeClass is run as static initializer, therefore it will run before the class instance of your test fixture is created.
5/2==2?
False
Static variables are always public, i.e. can be accessed outside of class.
True
A class can extend from 2 parent classes.
False
What interface does an object need to implement to be used in a TreeMap?
Map
Java does not allow a method with the same signature in a subclass, as a method in the super class
False. That is basically what overloading is.
A single JButton can have more than 1 ActionListener
False
Convert the string "50" into the number 50.
Integer.parseInt("50");
Doing string1.equals(string2) is the same as doing string2.equals(string1)
False
Which data structures implement the Collection interface?
Array; LinkedList; or Set Not HashMap
An ArrayList can contain primitive data types
True
You can have two overloaded methods with a di erence only in the return type.
False. To overload the methods you have to have a di erence either in name or argument types or number of arguments
Section 2
(21 cards)