Develop Reference

Can we use Setter Method in java to perform operations?

Is setter method only use to assigning values? or can we perform operations in it. Here in this code the commented part is giving me correct output but while using set and get I am getting output as 0.
I want to avoid calling totalMarksOfStudent() method again and again because it have 5 parameters which I dont want to give again and again. So what is the way to return totalMarksStudent in another class without calling totalMarksOfStudent().
int totalMarksStudent = 0;
public void setMarks(int englishMarks, int mathsMarks, int physicsMarks, int chemistryMarks, int csMarks) {
totalMarksStudent = englishMarks + mathsMarks + physicsMarks + chemistryMarks + csMarks;
}
public int getMarks(){
return totalMarksStudent;
}
// public int totalMarksOfStudent(int englishMarks, int mathsMarks, int physicsMarks, int chemistryMarks, int csMarks) {
// totalMarksStudent = englishMarks + mathsMarks + physicsMarks + chemistryMarks + csMarks;
// return totalMarksStudent;
}
public String displayTotalMarks() {
String totalMarks1 = "Name " + name + "\tRoll No " + rollNo + "\tTotal Marks " + getMarks();//totalMarksOfStudent(englishMarks, mathsMarks, physicsMarks, chemistryMarks, csMarks);
return totalMarks1;
}

Better to avoid that...
I think it's better to have some fields like your parameters in setMarks (englishMarks , mathsMarks , ...) , and give value to them in constructor or setter methods. Also it's better to have a method named something like calculateTotalMarks , and call it without any parameters whenever you need it. Remember that there will be no problem to have operations in setter methods but usually and for better designed program we avoid that. Methods should do the thing their name says : for example , setter just for assigning , getter just for accessing values , calculateTotalMarks for calculating the total marks and so on ...

setter method is usually used to assigning values. It is promise.
You can reduce parameters by using Object
I recommend to make object of MarksStudent. because common attribute can bind to one class. It make understand easily code
for example
// Java is object-oriented language
class marksStudents {
private int english;
private int math;
private int physics;
private int chemistry;
private int cs;
//getMethods is Abbreviation
public int getTotal() {
return english+math+physics+chemistry+cs;
}
//setMethods
public void setEnglish(int english) {
this.english = english;
}
public void setMath(int math) {
this.math = math;
}
public void setPhysics(int physics) {
this.physics = physics;
}
public void setChemistry(int chemistry) {
this.chemistry = chemistry;
}
public void setCs(int cs) {
this.cs = cs;
}
}
To execute
public class Main{
public static void main(String[] args) {
// You can make object marksStudents of studentsA
marksStudents studentsA = new marksStudents();
studentsA.setChemistry(20);
studentsA.setEnglish(30);
studentsA.setMath(40);
studentsA.setCs(50);
studentsA.setPhysics(60);
//200
System.out.println(studentsA.getTotal());
// You can make object marksStudents of studentsB too
marksStudents studentsB = new marksStudents();
studentsB.setChemistry(10);
studentsB.setEnglish(10);
studentsB.setMath(10);
studentsB.setCs(10);
studentsB.setPhysics(10);
//50
System.out.println(studentsB.getTotal());
}
}

The getter/setter method is only a practice. Not bad practice - it just defines a class, whose instances for the external world are handled by a list of independent values. Using them makes your code better comprehensible and easy to understand, what is it doing.
So it is no problem to make other operations with it, in general.
Some frameworks like to use reflection to use getters/setters and also reach the variables directly in them. In these cases, doing any different in the getters/setters than reading/writing the private members is no wise idea. Sometimes you can use a little bit of api/impl interface trickery to handle this problem.

Java return multiple strings in one method

I am attempting to write a program which asks users what their pet name is, species, finds out thirst level and gives a response accordingly.
I would appreciate if someone could help me with a problem im having, in each of the 2 methods askpetname and thirstlevel there are 2 strings i want accessible throughout the entire class without using global variables.
Can someone tell me what it is i am doing incorrectly or point me in the right direction.
Also, i understand that my excess use of methods for tedious tasks is bad practice but it helps with memorising syntax.
Thanks.
class dinoo
{
public static void main(String[] p)
{
explain();
output();
System.exit(0);
}
public static void explain()
{
print("The following program demonstrates use of user input by asking for pet name.");
return;
}
public static String askpetname()
{
Scanner scanner = new Scanner(System.in);
print("Name your dinosaur pet!");
String petname = scanner.nextLine();
print("Awesome, cool dinosaur name, what species is " + petname+ " ?");
String petspecies = scanner.nextLine();
return petname, petspecies;
}
public static int thirstlevel()
{
Random ran = new Random();
int thirst = ran.nextInt(11);
int hunger = ran.nextInt(11);
return thirst,hunger;
}
public static String anger(int thirst, int hunger)
{
double angerscore = (thirst+hunger)/2;
String temper;
if(angerscore<=2)
{
temper = "Serene";
}
else if(3<=angerscore<=6)
{
temper= "Grouchy";
}
else if(6<angerscore)
{
temper = "DANGEROUS";
}
return temper;
}
public static String warning()
{
if (temper.equals("Serene"))
{
print("He's looking happy!");
}
else if(temper.equals("Grouchy"))
{
print("Ahhh hes a bit "+temper+", you better start feeding him before he gets mad!");
}
else if(temper.equals("DANGEROUS"))
{
print("GET OUT OF THERE, HES " + temper+"!!!. He will have to be put down for everyones safety.");
}
}
public static void output()
{
print(askpetname() + "'s, thirst level is "+thirstlevel()+"/10");
return;
}
public static String print(String message)
{
System.out.println(message);
return message;
}
}

That code won't compile since you can't have:
return string1, string2;
or
else if(3<=angerscore<=6)
Instead of trying to return multiple Strings, your best bet is to create a class, say called Pet, one that holds String fields for the pet's name, a Species field for its species, as well as any other fields for hunger, thirst ... that would best encapsulate all the data that makes up one logical "pet" as well as a methods such as getAnger() that returns a value for anger depending on the Pet's state. Then you can create and return a viable Pet object from your creational method.
Also, your code has lots of compilation errors, suggesting that you could improve the way that you create your code. Never try to add new code to "bad" code, to code that won't compile. If possible, use an IDE such as NetBeans, Eclipse, or IntelliJ to help you create your programs. The IDE's will flag you if any of your code contains compilation errors, and then the key is: don't add new code until you've first fixed the existing compilation error. If you can't use an IDE, then you must compile early and often, and do the same thing -- fix all errors before adding new.

First, I would recommend shooting through a tutorial first before attempting this, do all the hello worlds covering scope, objects, arrays and functions. Get familiar with Object Oriented Style, although thats not even procedural programming ... nothing returns 2 objects ... always 1 (it could be an array containing many objects, but an array is a single object)
Moving on,although this is terrible coding practice, but its ok for a beginner,since your functions are all static, create a private static variable inside each function and create getter functions
//convert
String petname = scanner.nextLine();
// To this
private static String petname = scanner.nextLine();
// Then add this below it
public static String getPetName()
{
return petname;
}
and same for every piece of data you need.
Now remove the return statement from all of your functions and declare return type as void
Then call all functions from Main,
askpetname();
thirstlevel();
then print final output (after you have called the functions) as such
System.out.println("Petname: " + getPetname + " ThirstLevel: " + getThirstLevel() + " HungerLevel: " + getHungerLevel);

Basics of manipulating variables in different classes

I've done quite a bit of digging and can't seem to find the answer I'm looking for, I may be asking the question wrong because I'm pretty nooby.
Anyway I'm trying to build a simple Pokemon style game for practice and I can't seem to get the opponent or player hit points to change during the combat event..
I have it so you select 1. to attack with the following code:
if(select == 1){
System.out.println("You strike at the raccoon!");
System.out.println("You deal " + play1.atk + " damage!");
Math.subtract(raccoon1.hp, play1.atk);
the Math.subtract class is just
public static int subtract(int x, int y){
return (x-y);
}
Where it pulls raccoon1.hp from an object I built from an 'Opponent' class that just has:
public class Opponent {
public int hp = 5;
public int def = 0;
public int atk = 1;
}
The player is set up the same way.
I'm sure I'm just missing and/or doing something dumb but any help to a new programmer would be greatly appreciated.
Thanks!

Racoon1.hp = Math.subtract(raccoon1.hp, play1.atk)
You have to set the returned value equal to raccoon.hp, or else there's no point in returning a value.

This is a question of proper object-oriented programming. Instead of thinking about it in terms of variables, think about it in terms of methods. Don't try to manipulate the variable directly, try to manipulate it through operations done by the class.
In your case...
if(select == 1){
System.out.println("You strike at the raccoon!");
System.out.println("You deal " + play1.atk + " damage!");
//reduce the health by the current attack value of the player
racoon.reduceHealth(play1.getAttackValue());
In your Pokemon class, or whatever you named the class that you instantiate an instance of when creating a new Pokemon, create a method like this...
public void reduceHealth(int attackValue){
this.hp = this.hp - attackValue;
}
In your Player class, or whatever you named that class that you instantiate an instance of when creating a new Player, create a method like this...
public int getAttackValue(){
return this.atk;
}
This way, operations done on your objects are done so by its own class, not other classes. When getting information, create methods that return the information you want. When manipulating a variable of an object, use methods of the object to do the manipulation.

I suggestions you todo somethings like that
public class Opponent {
public int hp = 5;
public int def = 0;
public int atk = 1;
public void attack(Opponent target){
target.hp -= atk;
}
}
After you can simply do
Opponent player = new Opponent ();
Opponent badGuy = new Opponent ();
player.attack(badGuy);

Error: Constructor Room in class Room cannot be applied to given types

I am completely new to java. I have searched for hours upon hours for the solution to this problem but every answer involves passing args or using a void which I do not do in this situation.
I have two java files, one for Room class, and one for TourHouse class. I am trying to create a new Room in the TourHouse class. Here is my error, it's driving me nuts, I've tried everything I am capable of understanding. Thank you in advance.
HouseTour.java:15: error: constructor Room in class Room cannot be applied to given
types;
{
^
required: String, String
found: no arguments
reason: actual and formal arguments differ in length
Here is the Room class, will have 7 rooms total once I can figure this out
// Room.java
import java.util.*;
public class Room
{
// Define Instance Variables
private String name;
private String description;
// Define Constructor
public Room(String theName, String theDescription)
{
name = theName;
description = theDescription;
}
public String toString( )
{
return "The " + name + "\n" + description + "\n";
}
}
Here is the HouseTour class
import java.util.*;
public class HouseTour extends Room
{
// Define Variables
public Room[ ] rooms = new Room[7];
//Define Constructor
public HouseTour( )
{
rooms[0] = new Room("Living Room", "Mayonnaise and Brill Grates, Michaelsoft");
rooms[1] = new Room("Basement", "Hopefully no dead bodies down here...");
}
// this is horrible and not right
public String rooms( )
{
for (int i = 0; i <=7; i++)
{
String output = "House Rooms included in tour\n";
String output2 = output + rooms.toString() + "\n";
return output2;
}
}
}
EDIT: Solved but still need help here because I am complete n00b, :(
// this is horrible and not right
public String rooms( )
{
output = "House Rooms included in tour\n";
for (int i = 0; i <=7; i++)
{
output += rooms[i]; // I can't do this but how do i?
}
return output.toString(); // do I do this?
}
}
What I am doing is trying to learn java by converting the ruby projects I have created. So in ruby you say:
def rooms
output = "House Rooms included in tour\n"
#rooms.each do |r|
output += r.to_s + "\n"
end
return output
end
Edit: Still trying, any ideas?
added public String s; and public String output; to declarations
// this is horrible and not right
public String rooms( )
{
s = ""
output = "House Rooms included in tour\n";
for (int i = 0; i <=7; i++)
{
s += rooms[i];
}
s.toString() // I don't know
return output + s; // do I do this?
}
}
Edit: Solved thanks to Hovercraft Full Of Eels

Ah, I see your problem: HouseTour extends Room. Don't do this! HouseTour is not a more specific case of a Room type and so should not extend this class. It does not fulfill the "is-a" rule, and would be similar to trying to define Bus as a child class of SchoolKid. Just like a Bus isn't a type of SchoolKid but rather contains SchoolKids, a HouseTour isn't a Room but rather contains Rooms. It fulfills the has-a relationship, not the is-a relationship.
If the inheritance were proper in this situation, your HouseTour constructor would need to call the Room super constructor and pass in two String parameters:
// Don't do this!!!
public class HouseTour extends Room {
public HouseTour() {
super("foo", "bar");
....
}
But having said that, again inheritance is not proper here -- just get rid of extends Room, and you're home free.
e.g.,
public class HouseTour { // no extends!
private Room[] rooms; // has-a not is-a
public HouseTour() {
// don't call super here
}
Also, as per my comment, this will give you ugly output: rooms.toString()
Instead iterate through the Array and get the toString() result from each Room item in the array.
Edit
Suggestions on your rooms() method:
Create a String or StringBuilder before the loop.
Build up the String or StringBuilder inside the loop.
Return the String or StringBuilder#toString after the loop.
Inside of the loop get the toString() from the current Room item in the list.
You will need to check that the rooms[i] item isn't null before calling a method on it.
Edit 2
You state that this:
public String rooms( )
{
output = "House Rooms included in tour\n";
for (int i = 0; i <=7; i++)
{
output += rooms[i]; // I can't do this but how do i?
}
return output.toString(); // do I do this?
}
is causing problems, but you don't specify the problem.
Myself, I'd do something like:
public String rooms( ) {
// declare your String locally, not globally in the class
String output = "House Rooms included in tour\n";
// again, avoid using "magic" numbers like 7
for (int i = 0; i < rooms.length; i++) {
output += rooms[i].toString(); // **** you must extract Room's String
}
return output; // no need to call toString() on a String
}

extending a class with an extra parameter

I got a simple question. I have a class, which I use for purpose of splitting a string in 2 years:
public class Period {
int firstYear;
int secondYear;
Period () {
}
Period(String periode) {
String [] periodeSplit = periode.split("-");
this.firstYear = Integer.parseInt(periodeSplit[0]);
this.secondYear = Integer.parseInt(periodeSplit[1]);
}
public String toString() {
return "Firstyear: " + this.firstYear + "\n" + "Secondyear: " + this.secondYear;
}
}
I now want to extend this class, not splitting the data into 2 different ints but into 3 different ints. So besides the 2 already exisiting integer vars I want one extra. Whats the easiest way of doing this?
Your help is appreciated!
Kind regards,
Kipt Scriddy

I think it would be better (and quite easy) the create more general class that will be able to deal with any number of years you pass to it:
public class Period {
int[] years;
Period() {
}
Period(String periode) {
String[] periodeSplit = periode.split("-");
years = new int[periodeSplit.length];
for (int i = 0; i < periodeSplit.length; i++) {
years[i] = Integer.parseInt(periodeSplit[i]);
}
}
public String toString() {
String result = "";
for (int i = 0; i < years.length; i++) {
result += "Year " + i + ":" + years[i] + "\n";
}
return result;
}
}
If the original class really have to be extended than it can be done like this:
class ExtendedPeriod extends Period {
int thirdPart;
ExtendedPeriod(String periode) {
String[] periodeSplit = periode.split("-");
this.firstYear = Integer.parseInt(periodeSplit[0]);
this.secondYear = Integer.parseInt(periodeSplit[1]);
this.thirdPart = Integer.parseInt(periodeSplit[1]);
}
public String toString() {
return "Day: " + this.firstYear + "\n" + "Month: " + this.secondYear
+ "\nYear: " + this.thirdPart;
}
}
I would recommand to change variable names 'firstYear' and 'secondYear' to something different, like 'firstPart', 'secondPart' because for extendedPeriod they aren't years anymore (I left them in my code so it would compile with yours but called the new int 'thirdPart'). I don't feel that this is the best use of inheritance but if that's what's needed. I also wanted to reuse toString from Period like this:
public String toString2() {
return super.toString() + "\nThird part: " + this.thirdPart;
}
but for it to have sense you would have to chagne toString method in Period not to call values 'years'.

When you extend the class, split it into two variables first, the one that's different from your current code, and then the one that your current code would handle.
Then simply call super(periode)
The child class will have access to the parent variables, since you made them default.

I wouldn't extend to just add a new year.
Why not make the entire thing generic enough, so that it supports whatever split you need.
public class Period {
String [] periodeSplit;
Period(String periode) {
periodeSplit = periode.split("-");
}
public String toString() {
//TODO : Iterate and print.
}
}