Procedural Programming

Question 1

What is a computer program?

Answer 1

Collection of instructions that performs specific task when executed by comp, tells comp what to do, step by step. Rep of algorithm. To run it, we need a few things: editor, source file (.java), compiler, class files (.class), virtual machine + library files.

Question 2

What is the case if there are errors at the compilation stage?

Answer 2

Compilation can’t take place.

Question 3

What is a .class file?

Answer 3

Can be read by any device capable of interpreting/translating file into something it can run. Platform independent so portable. Class file name must match that of Java program you are coding. First letter should be uppercase.

Question 4

What is a virtual machine?

Answer 4

Reads + runs .class file.

Question 5

How do you instruct the comp to do something?

Answer 5

Use statements, like declaration, assignments or method calls. To instruct to do something multiple times, use loops such as for, while or do. If you want it do something based on a condition, use if else, switch or nested loops.

Question 6

What are the reasons to have the main method as public and typing static + void after it?

Answer 6

Public allows everyone to access it so it can be seen + run. Static identifies that it isn’t related to an object + void tells comp that nothing needs to be returned from method.

Question 7

Why do we type String [] args?

Answer 7

This relates to parameters the method requires. A string array will be referred to variable name “args”.

Question 8

What is the Scanner used for + how do we access it?

Answer 8

Required import from standard Java libraries, java.util, which allows user to input data from console. Import statements must be at top of file. Must set up Scanner variable called userInput so we can store input. Must then set up int/double variable to read this info. We then code nextInt() method which saves input to variable. Must close scanner using userInput.close();

Question 9

What should we do when taking user input?

Answer 9

Check user has entered correct data as users easily make mistakes.

Question 10

What is JOptionPane used for + how do we access it?

Answer 10

Displays data + allows user input. Must import from Java libraries (import javax.swing.JOptionPane. To show data, use JOptionPane.showMessageDialog(null, “Message”);. To get input, String name = JOptionPane.showInputDialog(“Question: “);

Question 11

What are the 3 steps of programming?

Answer 11

Design, commenting in java + coding + compiling + running code. Could encounter errors while compiling + running code so we must return to fix bugs as java is case sensitive.

Question 12

What is a syntax error?

Answer 12

AKA compile time error. Not including semicolon, incorrect spelling, leaving out “ or not matching {} or (). The compiler will flag up these errors.

Question 13

What is a runtime error?

Answer 13

AKA logic error. Incorrectly spelling statements in quotations, trying to do impossible calculation or referring to undefined value. Harder to trace as compiler won’t flag them up. Some runtime errors are so extreme that they generate an exception e.g. dividing by 0.

Question 14

What is an algorithm?

Answer 14

Series of steps which help us to find solution to problem. Must first design on paper. Must be unambiguous, executable + terminating. We use pseudocode before writing actual program and after writing algorithm. Doesn’t have strict requirements as read by humans, not comp.

Question 15

What is a variable?

Answer 15

Container to hold info that will change throughout program. Must include name + type when declaring them. Each type has associated size. Beware of overflow. 2 categories of variable types: primitive + non primitive. First letter should be lowercase + not start with nums. Use camel naming method + don’t use reserved words.

Question 16

What is a primitive type?

Answer 16

Predefined by language + named by reserved keyword. Don’t share space in memory with other primitive values. 8 types: byte, short, int, long, double, float, boolean + char.

Question 17

What are the 4 integer types?

Answer 17

Byte, short, int + long.

Question 18

What are the 2 floating point types?

Answer 18

Double + float.

Question 19

What are the 2 non number related primitive types?

Answer 19

Boolean (1 bit) + char (2 bytes, 16 bits)

Question 20

Describe double type.

Answer 20

All transcendental math functions return double values {-sin;, cos();, sqrt();} Double is best choice when need accuracy over many iterative calcs or when manipulating large nums. To express, e.g. double d1 = 123.4; For scientific notation, double d2 = 1.234e2

Question 21

Describe float type.

Answer 21

Faster on some processors (takes up half space as double + imprecise when values very large/small). Useul when need fractional component but don’t require it to be very precise. e.g. fuel price. To express, e.g. float f1 = 123.4f

Question 22

How do you declare char values?

Answer 22

Enclose in single quotes, any printable character e.g. char initial = ‘n’ or ‘+’. Anything in unicode.

Question 23

How do you declare a boolean value?

Answer 23

No null value, no numeric equivalent. Boolean isHappy = true; Must be lowercase.

Question 24

How do we convert a floating point num to an integer?

Answer 24

Using casting. Must be done this way as fractional part is lost + magnitude may be too large so java won’t let you do it normally. e.g. int myInt1 = (int)myDouble1

Question 25

What are some examples of reserved words you can’t use when declaring variables?

Answer 25

Any of the data types, catch, continue, extends, final, if, package, super, private, try + while.

Question 26

What is another way of typing -1 or +1 in java?

Answer 26

Type variable – or variable ++

Question 27

What happens if you mix integer + floating point variables in an arithmetic expression?

Answer 27

You get a floating point number.

Question 28

To find the remainder when dividing, what must we do?

Answer 28

Instead of using mod, we use % e.g. 7%4 = 3.

Question 29

How do we find the root of a number?

How do we find the note the power of a number?

Answer 29

Math.sqrt(x);

Math.pow (x,n);

Question 30

How do we find the length of a string?

Answer 30

int n = stringName.length(); A string of length 0 is empty + denoted by “”.

Question 31

What is a string?

Answer 31

A set of unicode characters.

Question 32

How do you return a char value from a string?

Answer 32

Use charAt method e.g. char start = name.charAt (0); OR name.charAt(length-1);

Question 33

What is a substring?

Answer 33

Allow us to pick out parts of strings e.g. str.substring(start, pastEnd); \n String name = “Hello W”; \n String sub = name.substring (0,5); to give us Hello

Question 34

How can we include a quotation mark in a string?

Answer 34

We can use \ e.g. “He said "Hello"”. We can also use backslash for file references + take a new line using \n.

Question 35

What is an exception?

Answer 35

An error message from Java Virtual Machine.

Question 36

How might we swap the values of 2 variables?

Answer 36

Create a temp variable and place one of the values into it while you swap them. e.g. a=1, b=2, temp=a, a=b, b=temp.

Question 37

How would you code this in java:
b x (1 +r/100)^n

Answer 37

b * Math.pow(1+r/100,n)

Question 38

What is the point of selection in java?

Answer 38

We need selection to choose between alternative courses of action.

Question 39

What is an if statement?

Answer 39

It’s the most basic selection statement, it tells the program to execute a certain code section if a particular thing is true. Ensure to use indentation and curly brackets around the conditional code.

Question 40

What are the 3 logic operators + what can they be used on?

Answer 40

And, or + not. And = &&. Or = ||. Not = !. Can be used on boolean + string.

Question 41

How do we compare floating point numbers?

Answer 41

We are careful of roundoff errors so find out if they are approximately equal. We test if difference is less than a certain small threshold value, usually called epsilon.
e.g. final double EPSILON = 1E-14;
if (Math.abs (x-y) <= EPSILON) {}

Question 42

How do we test if 2 strings are equal?

Answer 42

Use if(string1.equals(string2))

Question 43

How do we compare 2 strings?

Answer 43

Compare in lexicographic order. string1.compareTo(string2)

Question 44

When comparing strings, what do the answers we get mean?

Answer 44

If the answer is less than 0, string 1 comes before string 2. If the answer is 0, they are equal. If the answer is more than 0, string 2 comes before string 1.

Question 45

What is lexicographic order?

Answer 45

Space comes first, then numbers, then uppercase letters, then lowercase letters. Punctuation is found throughout the lexicographic order.

Question 46

What are flowcharts used for?

Answer 46

Illustrate structure of decisions + tasks required to solve problems.

Question 47

How do you avoid spaghetti code?

Answer 47

Never point an arrow inside another branch.

Question 48

What is a local variable?

Answer 48

A variable declared inside a block of an if statement. Can’t be used or seen anywhere else.

Question 49

What is a global variable?

Answer 49

Declared outside of an if statement and can be used everywhere, including inside if statements.

Question 50

What are enumeration types?

Answer 50

Hold one of finite num of values called enumeration/enum constants. Must be unique. Can only declare one of values held in enum type.
e.g. public ENUM FilingStatus {SINGLE, MARRIED} FilingStatus status = FilingStatus.SINGLE;

Question 51

What is a method?

Answer 51

Collection of grouped statements to perform operations. Can be called elsewhere in program. Each consists of method header + body. Can’t define method inside another method. One method can call another method.

Question 52

What are methods for?

Answer 52

Reduce code duplication, improve code efficiency + reduce code defects.

Question 53

Give an example of a method declaration.

Answer 53

E.g. public static int addTwoNums(int x, int y){int sumTwoNums = x + y; return sumTwoNums;}

Question 54

What are the 3 types of methods?

Answer 54

Void method without parameters, void method with parameters + parameterised method with return type.

Question 55

What is a void method without parameters?

Answer 55

Executes set of instructions, needs no parameters (info) to work + no expectation to return anything once method executed.

Question 56

What is a void method with parameters?

Answer 56

Executes set of instructions using parameters provided, nothing returned once executed.

Question 57

What is a parameterised method with return type?

Answer 57

Executes set of instructions using parameters provides, single variable of specified data type returned once method executed.

Question 58

What is a variable’s scope?

Answer 58

Where in program it’s visible. Variables defined in diff methods have diff scopes.

Question 59

What is the Java API?

Answer 59

Application Programming Interface. Can find out info about standard classes + methods by looking it up.

Question 60

Where should you always put comments?

Answer 60

Before all constructors and methods.

Question 61

What are the 3 main parts of loops? (Especially while loops)

Answer 61

The test (logical Boolean), the statements to be repeated + how the test will be updated so it isn’t an infinite loop.

Question 62

How do we create for loops?

Answer 62

Initialise counter, check condition, execute loop body, update counter + check condition again.

Question 63

What is the difference between for loops + while loops?

Answer 63

While loops are event controlled + indefinite but for loops are count controlled + definite.

Question 64

What are do loops for?

Answer 64

Execute body of loop at least once before testing condition. e.g. input validation

Question 65

What is a break statement?

Answer 65

Terminates a loop, used to break out of loop.

Question 66

What is a continue statement?

Answer 66

Jumps to end of current loop iteration.

Question 67

What are sentinel values?

Answer 67

If reading sequence of inputs, need to indicate end of sequence using this. E.g. -1.

Question 68

What should you be aware of when computing averages?

Answer 68

Ensure count is not 0.

Question 69

How do we compare adjacent values?

Answer 69

Use previous.

Question 70

When can we use an array and what is it?

Answer 70

If the values are related, we can use an array. This allows us to hold more than one value at a time, it is one variable. It needs a name and a type.

Question 71

How do we initialise an array?

Answer 71

When initialising then array, it is good to use a constant rather than a magic number to declare the size.
Each element of the array receives a default value. Primitive = 0, Boolean = false, object = null.

Question 72

How do we add values to fixed length arrays?

Answer 72

Arrays are fixed length so can’t add extra values. We can copy it into a new array to fix this. Arrays start at 0 so if it is length 10, then accessing 10th variable won’t work. We can use .length to check number of values.

Question 73

How do we print out the values of an array?

Answer 73

We use a for loop to print out all elements of the array.

Question 74

What can arrays be?

Answer 74

Arrays can be method arguments or return values. Therefore, if you define a method with an array parameter, you must provide an array as the argument variable.

Question 75

What is true of the size of arrays?

Answer 75

An array can’t change size at run time. If you have an array where you need at least 10 and no more than 100, this is going to be a partially filled array so you need a variable to determine how many elements are currently stored in the array.

Question 76

What are parallel arrays?

Answer 76

If you want to store data of a different meaning, use parallel arrays e.g. with age + shoe size at same position in diff arrays.

Question 77

What is a 2D array?

Answer 77

An array of arrays. E.g. double [] [] entries = new double [7] [3]

Question 78

What does str.split(“ “) do?

Answer 78

Breaks given string into array of substrings.

Question 79

What can we do if say 1 student sits 4 exams and another sits 6?

Answer 79

Use same method with diff num of arguments e.g. int…values. Values parameter is int [] array containing all arguments that were passed to method.

Question 80

How do you generate a random number?

Answer 80

To generate a random number between 0 and 1, use Math.random(). You can use this to fill an array with random values.

Question 81

What is an enhanced for loop?

Answer 81

Enhanced for loop is for (typeName variable : collection) {statements;}

Question 82

How do you remove an element in an array?

Answer 82

Removing an element in an unordered array can require a little more work, can overwrite element to be removed with last element of array, then decrement variable holding array size. If they’re ordered, must move all elements following element to be removed to lower index + decrement variable holding array size.

Question 83

How do you insert an element into an array?

Answer 83

When inserting elements, must ensure array is large enough. Can separate elements when printing by using for (int i = 0; I < values.length; i++) {for (i > 0) {System.out.print(“ | “);}System.out.print(values[i]);} For debugging, System.out.println(“Values = “ + Arrays.toString(values));

Question 84

Why might you use an array list?

Answer 84

If your program is collecting input + you don’t know how many elements there will be. They can grow + shrink as required. The ArrayList class supplies methods for common tasks like inserting & removing elements. ArrayList names = new ArrayList(); (must import.java.util.ArrayList)

Question 85

How do we add into an array list?

Answer 85

Can’t use primitive types (no int/double). To add, names.add(“Emily”); To get the elements, String name = names.get(2); To set an element to a new value, use names.set(2, “Carolyn”). Can insert element in middle of array list e.g. names.add(1, “Ann”). Moves elements of index 1 + up.

Question 86

How do we remove from an array list?

Answer 86

Remove method removes element at given position + moves all elements after it down by one. e.g. names.remove(2); To get the length, use names.size();

Question 87

How do we search for data in an array list?

Answer 87

search (index, data)