Ap Computer Science Midterm Practice Exam- Java Basics, Arrays Questions With 100% Correct Answers

Ap Computer Science Midterm Practice Exam- Java Basics, Arrays Questions With 100% Correct Answers Identity - ANSWER differentiates one instance from another (like an id number or location in memory) Class (OOP Definition #2) - ANSWER The code you write Defines an object's "state" (as variables) Defines an object's "behavior" (as methods, i.e. functions) "template" or "mold" for creating new objects Tells Java "how" to create an object Instance (OOP Definition #2) - ANSWER Instance = A single actual object "created" based on the template (the class) - the data+code that is actually stored in memory Maintains own "state" Exhibits own "behavior" Maintains own "identity" Two instances, like two cookies made from the same cookiecutter, are still different Referenced with the new keyword Getter - ANSWER A getter returns, or "gets" an instance to the main code. For example, in the rectangle project the user could set the value to whatever they wanted, and the getter method just returned that to the runner. Known as an accessor Setter - ANSWER Allows a user to set an instance, for example making the height of rect1 200. Known as a mutator Overloaded Constructor - ANSWER You can create an alternate Constructor that automatically sets your instance variables to specific starting values. Instead of making a setter for the values, you can put variables in your constructor that the user enters after the new keyword. String [] arr = new String [10]; how many strings are made? - ANSWER 0, all 10 strings created were set to null, therefore they are not real strings Can an Object or a Primitive Type be in an array? - ANSWER Both How do you declare a new array? - ANSWER type [ ] name = new type [number] or type name [ ] = new type [number] or int [ ] George = {1,2,3,4,} What is the name of a value at specific point in the array? - ANSWER Index nums [2] = 10; nums is the name, the index of this is 2, the value is 10 Enhanced For Loop - ANSWER Alternative for-loop to retrieve each item in an array one at a time - much more like for-loops in Python. Can you reference or declare an array in an enhanced for loop? i.e. (int arrVal : arr) { Sln(arr[arrVal]); } - ANSWER No, you can not. If you just call for printing arr, the for loop will go through all the values of the variable and print them. Overloaded Constructor - ANSWER A constructor that has parameters, set to the instance variables Default Constructor - ANSWER A constructor with no parameters that sets the instance variables to default values. i.e. Given an array of ints, return true if every element is a 1 or a 4. only14([1, 4, 1, 4]) → trueonly14([1, 4, 2, 4]) → falseonly14([1, 1]) → true - ANSWER public boolean only14(int[] nums) { for (int i = 0; i h; i++) { if (nums [i] != 1 && nums [i] != 4) { return false; } } return true; } Return the number of even ints in the given array. Note: the % "mod" operator computes the remainder, e.g. 5 % 2 is 1. countEvens([2, 1, 2, 3, 4]) → 3countEvens([2, 2, 0]) → 3countEvens([1, 3, 5]) → 0 - ANSWER public int countEvens(int[] nums) { int number = 0; for (int i = 0; i h; i++) { if (nums [i] % 2 == 0) { number = number + 1; } } return number; } What is true about local variables? l. Local variables can be declared in the body of constructors and methods. ll. Local variables may only be used within the constructor or method and cannot be declared to be public or private. lll. When there is a local variable with the same name as an instance variable, the variable name will refer to the local variable instead of the instance variable. - ANSWER All of the above are true Default value for a double in an array - ANSWER 0.0 Default value for an int in an array - ANSWER 0 Default value for a boolean in an array - ANSWER false Default value for a String in an array - ANSWER null Is it better to use a for loop or an enhanced for loop to print an array? - ANSWER Enhanced for loop Given an array of ints, return true if the number of 1's is greater than the number of 4's more14([1, 4, 1]) → truemore14([1, 4, 1, 4]) → falsemore14([1, 1]) → true - ANSWER public boolean more14(int[] nums) { int count1 = 0; int count4 = 0; boolean counter = false; for (int i = 0; i h ; i++) {