Distinguish between a class and an object

Transcription

1 Java Revision

2 Distinguish between a class and an object

3 Distinguish between a class and an object A class is the blueprint from which individual objects are created; And object is an instance of a class.

4 How would you declare a class called Square?

5 How would you declare a class called Square? class Square { }

6 How would you create an object, called yellowsquare of a class called Square?

7 How would you create an object, called yellowsquare of a class called Square? Square yellowsquare = new Square();

8 What is a Java method?

9 What is a Java method? A method describes an action that can be carried out on or by an object

10 How would you call a method called showsquare for an object called yellowsquare?

11 How would you call a method called showsquare for an object called yellowsquare? yellowsquare.showsquare();

12 From which method does the execution of a Java application start?

13 From which method does the execution of a Java application start? From method main

14 Write down the main method declaration

15 Write down the main method declaration public static void main (String args[]){ }

16 List three Java numeric variable types

17 List three Java numeric variable types long short byte int float double

18 Put the following Java primitive types in order, smallest first: int long byte short

19 Put the following Java primitive types in order, smallest first: byte short int long

20 How would you declare a Java variable called length? (Where length is the length of a window in metres)

21 How would you declare a Java variable called length? (Where length is the length of a window in metres) float length;

22 Declare a final variable called VAT whose value is 0.18

23 Declare a final variable called VAT whose value is 0.18 static final float VAT = 0.18;

24 Explain the function of this line: System.out.printf ("%1.2f", this.cost);

25 Explain the function of this line: System.out.printf ("%1.2f", this.cost); It outputs this.cost to two decimal places

26 Write a line that outputs The total is and the value of instance variable total on the screen.

27 Write a line that outputs The total is and the value of instance variable total on the screen. System.out.println( The total is: + this.total);

28 Write a method called outputtriangle that outputs the values of sides of a triangle object a, b and c.

29 Write a method called outputtriangle that outputs the values of sides of a triangle object a, b and c. public void outputtriangle(){ System.out.println ( Side a: + this.a); System.out.println ( Side b: + this.b); System.out.println ( Side c: + this.c); }

30 Write a method called getvatcost that calculates and returns the cost (VAT included) of an object passed to it (Assume VAT rate is stored in a global constant variable called VAT)

31 Write a method called getvatcost that returns the cost (VAT included) of an object (chair) passed to it (Assume VAT rate is stored in a global constant variable called VAT) public float getvatcost(){ float VATCost = (this.cost* VAT) + this.cost; return VATCost; }

32 Write a simple Java method called findarea that finds and outputs the area of a rectangle object of sides a and b

33 Write a simple Java method called findarea that finds and outputs the area of a rectangle object of sides a and b public void findarea() { float area = this.a * this.b; System.out.println ( Area : + area + sq cm ); }

34 Write a simple Java method called checkifoverdrawn that checks if an account is overdrawn and returns true or false accordingly.

35 Write a simple Java method called checkifoverdrawn that checks if an account is overdrawn and returns true or false accordingly. boolean checkifoverdrawn(){ if (this.balance<0){ boolean overdrawn = true; } else{ boolean overdrawn = false; } }

36 Implement a case/switch structure in a method (call your method makemenuchoice) that outputs the following Menu and then writes on the screen the name of the Menu Option chosen. Main Menu 1. Enter Student Details 2. View Classes 3. View Marks 4. View Prize Winners 5. Exit

37 Implement a case/switch structure in a method (call your method makemenuchoice) that outputs the following Menu and then writes on the screen the name of the Menu Option chosen. Main Menu 1. Enter Student Details 2. View Classes 3. View Marks 4. View Prize Winners 5. Exit public void makemenuchoice(){ System.out.println ( Main Menu ); System.out.println ( 1. Enter Student Details ); System.out.println ( 2. View Classes ); System.out.println ( 3. View Marks ); System.out.println ( 4. View Prize Winners ); System.out.println ( 5. Exit ); byte choice = input.nextbyte(); switch (choice) { case 1: { System.out.println ( Enter Student Details ); break; } case 2: [ etc ] } }

38 Name the three types of Java looping structures

39 Name the three types of Java looping structures for while do..while

40 Answer True or False A For Loop is a predetermined loop A do..while loop will loop 0 or more times A while..do loop will loop one or more times

41 Answer True or False A For Loop is a predetermined loop True A do..while loop will loop 0 or more times False A while..do loop will loop one or more times False

42 Write a method called handletest that reads 10 marks into an array called marklist. Write a method called findhighest that finds and outputs the highest mark in array marklist Write a method called findlowest that finds and outputs the lowest mark in array marklist Write a method called findaverage that finds and outputs the average mark in array marklist

43 Write a method called handletest that reads 10 marks into an array called marklist. public void handletest() { } int[] marklist = new int[10]; for (int i = 0; i<10; i++){ System.out.println ( Enter mark ); this.marklist[i] = input.nextint(); }

44 Write a method called findhighest that finds and outputs the highest mark in array marklist public void findhighest() { int i; int highest = 0; for (int i = 0; i <10; i++) { if (marklist[i] > highest){ highest = marklist[i]; } System.out.println ( The Highest Mark is + highest); } }

45 Write a method called findlowest that finds and outputs the highest mark in array marklist public void findlowest() { int i; int lowest = 100; for (int i = 0; i <10; i++) { if (marklist[i] < lowest){ lowest = marklist[i]; } System.out.println ( The Lowest Mark is + lowest); } }

46 Write a method called findaverage that finds and outputs the average mark in array marklist public void findaverage() { int total = 0; for (int i = 0; i <10; i++) { total = marklist[i] + total; //total+= marklist[i]; } double average = total/10; System.out.println ( The Average Mark is + average); } }

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