I have different fields using the same parameters i.e. same grading scale. I want to use switch statement to return grades for different fields using the same scale. Something like this. I thought that there was something like this: switch (attend, job, initiative) { that would combine the three variables.
int attend = 5;
int job = 5;
int initiative = 5;
switch (attend) {
case 1:
getattendo = 5;
break;
case 2:
getattendo = 4;
break;
case 3:
getattendo = 3;
break;
case 4:
getattendo = 2;
case 5:
getattendo = 1;
break;
default:
getattendo = 0; // null
}
Your help is appreciated.
fmk
Enum works well with switch cases. So, you can define an enum that represents your range of value of it is a finite and reasonable range of values :
public enum OPTIONS {
OPTION1(5, 5, 5),
OPTION2(5, 2, 4),
OPTION3(1, 2, 3),
OPTION4(4, 4, 1);
private final int attend;
private final int jobs;
private final int initiative;
Directive(int attend, int jobs, int initiative) {
this.attend = attend;
this.jobs = jobs;
this.initiative = initiative;
}
// ... optional setters & getters
}
Given your create OPTION Enum, you can use a switch to handle the different cases :
switch (OPTION) {
case OPTION1:
getattendo = 5;
break;
case OPTION2:
getattendo = 4;
break;
case OPTION3:
getattendo = 3;
break;
case OPTION4:
getattendo = 2;
break;
default:
getattendo = 0; // null
break;
}
Note: Your switch is legitimate only if you have a finite number of condition. Otherwise, use a method to calculate your result.
A trick you use utilizes the unary or operation for checking binary digit presence.
This will help get you started on switching according to various conditions.
This is similar to how file permissions work in Linux.
public class ScoreCombinator {
public static final int ATTEND = 1; // binary: 001
public static final int JOB = 2; // binary: 010
public static final int INITIATIVE = 4; // binary: 100
public static void main(String[] args) {
evaluate(ATTEND | INITIATIVE); // Attend and Initiative
evaluate(INITIATIVE | ATTEND | JOB); // Attend, Job, and Initiative
}
private static void evaluate(int value) {
switch (value) {
case ATTEND: {
System.out.println("Attend");
break;
}
case ATTEND | JOB: {
System.out.println("Attend and Job");
break;
}
case ATTEND | JOB | INITIATIVE: {
System.out.println("Attend, Job, and Initiative");
break;
}
case ATTEND | INITIATIVE: {
System.out.println("Attend and Initiative");
break;
}
case JOB: {
System.out.println("Job");
break;
}
case JOB | INITIATIVE: {
System.out.println("Job and Initiative");
break;
}
case INITIATIVE: {
System.out.println("Initiative");
break;
}
}
}
}
Something like switch(a,b,c) is not possible.
If all values are the same, just use one of the valueslandmaybe verify that all values are the same).
However, there are workarounds if you want to switch-case with multiple numbers:
mathematical solution
For example, you could use prime numbers for this. As you only want to switch numbers, this is possible as long as there is a prime number higher than the highest expected value(for attend, prime and job).
Instead of switch(attend, job, initiative), you use switch((attend*prime+job)*prime+initiative) and instead of case (exampleAttend, exampleJob, exampleInitiative):, you use case ((exampleAttend*prime+exampleJob)*prime+exampleInitiative):
Note that prime must be the same in the switch and case statements.
Note that you should test if any of the input numbers is higher than the prime. This would logically lead to the default case but it could lead to collissions.
You may also want to make sure that the prime to the forth power is lower than the max value of the data type or there may be overflows.
On the other side, this method should be more performant than the second.
simple string concadation
Another option is to work with strings. As the string representation of a number is unique (to the number) and it does not contain some characters (like spaces), you can concadate those numbers and use such a character to seperate them.
Instead of switch(attend, job, initiative), you use switch(attend+" "+job+" "+initiative) and instead of case (exampleAttend,exampleJob,exampleInitiative):, you use case (exampleAttend+" "+exampleJob+" "+exampleInitiative):.
This is obviously easier and fail-safer than the first method involving prime numbers but there should be a performance impact as concadating strings is slower than multiplying ints.
Another possibility is to use enums. Look at the other answer by #Hassam Abdelillah
if you want to know how this works. If you like the enum approach, feel free to upvote the other answer.
Related
Can I use the same number for 2 cases in a switch statement in old versions in Java?
int rand = 3;
switch(rand)
{
case 3: System.out.print("***");
case 3: System.out.print("###");
default: System.out.println("&&&");
}
I am using the Java version 15.0.1 and it is not working.
This will not be possible as switch needs a single option for a particular input. You can either use one option like below.
int rand = 3;
switch(rand)
{
case 3: System.out.print("***");
default: System.out.println("&&&");
}
or concatenate both together like below
int rand = 3;
switch(rand)
{
case 3: System.out.print("***###");
default: System.out.println("&&&");
}
Good Evening,
I created this method for a class. I used a switch/case to execute depending on the value of expression. I included an if-else method for each case. I do get an error on case 1-> switch rules are a preview feature and are disabled by default. I attempted to add a : after case 1 and case 2but my results reached high numbers for the sets. I changed the : to -> and it worked appropriately. Now I am wondering if this was a proper way to set the case statements or should it be written differently.
private void playGame()
{
double winCheck = Math.random();
switch (matchServer) {
case 1 ->{
if (winCheck <= player1WinProb)
player1GamesWon++;
else
player2GamesWon++;
matchServer = 2;
}
case 2 ->{
if (winCheck <= player2WinProb)
player2GamesWon++;
else
player1GamesWon++;
matchServer = 1;
A correct switch statement must use ':'
Also, 'break' is missing. This to avoid executing next cases.
You can add 'default' that means that case 1 and case 2 were not presented.
switch (matchServer) {
case 1:
if (winCheck <= player1WinProb)
player1GamesWon++;
else
player2GamesWon++;
matchServer = 2;
break;
case 2:
if (winCheck <= player2WinProb)
player2GamesWon++;
else
player1GamesWon++;
matchServer = 1;
break;
default:
//If it was not 1 or 2
//Printing the values can help
}
I have a chunk of code that needs to determine if a given integer is between a set of other integers. I'd also like to have this in a case statement so as to not have a surplus of if..else statements everywhere. Here's a bit of the code:
switch (copies) {
case copies >= 0 && copies <= 99: copyPrice = 0.30; break;
case copies >= 100 && copies <= 499: copyPrice = 0.28; break;
case copies >= 500 && copies <= 749: copyPrice = 0.27; break;
case copies >= 750 && copies <= 1000: copyPrice = 0.26; break;
case copies > 1000: copies = 0.25; break;
}
where copies is an integer and copyPrice is a double. I get several errors saying that it expects to receive a integer but gets a boolean instead. What is the best (or optimal) way of setting this up? Any help is greatly appreciated!
This line (and similar):
case copies >= 0 && copies <= 99:
Returns a compiler error since it gives a boolean but the compiler expects an int since copy is declared as int.
One way to solve this is using an array with the desired ranks, and have a switch statement for the index found:
public double calculateCopyPrice(int copies) {
int[] range = { 99, 499, 749, 1000 };
double copyPrice = 0;
int index = -1;
for (int i = 0; i < range.length; i++) {
if (range[i] >= copies) {
index = i;
break;
}
}
switch (index) {
case 0: copyPrice = 0.30; break;
case 1: copyPrice = 0.28; break;
case 2: copyPrice = 0.27; break;
case 3: copyPrice = 0.26; break;
default: copyPrice = 0.25; break;
}
//probably more logic here...
return copyPrice;
}
After some tests, I've found a more flexible solution using a TreeMap<Integer, Double> which allows you to have a specie of range (what you're looking for) and ease the search by using TreeMap#ceilingEntry:
//TreeMap to store the "ranges"
TreeMap<Integer, Double> theMap = new TreeMap<Integer, Double>();
//add the data
theMap.put(99, 0.3);
theMap.put(499, 0.28);
theMap.put(749, 0.27);
theMap.put(1000, 0.26);
//the "default" value for max entries
theMap.put(Integer.MAX_VALUE, 0.25);
//testing the solution
Double ex1 = theMap.ceilingEntry(50).getValue();
Double ex2 = theMap.ceilingEntry(500).getValue();
Double ex3 = theMap.ceilingEntry(5000).getValue();
Double ex4 = theMap.ceilingEntry(100).getValue();
System.out.println(ex1);
System.out.println(ex2);
System.out.println(ex3);
System.out.println(ex4);
java has no native concept of "ranges", let alone support for them in case statements.
usually, when faced with this kind of logic i personally would do one of 2 things:
just have a chain of if-else statements. doesnt even habe to be a chain:
public static double calculateCopyPrice(int copies) {
if (copies > 1000) return 0.25;
if (copies >= 750) return 0.26;
//etc
}
this code has no "else" branches and is just as much typing as the switch syntax you'd like. possibly even less (i only check a single bound every time)
you could use an enum, say:
public enum Division {UNDER_100, 100_to_500, ... }
and then :
Division division = categorize(copies);
switch (division) {
case UNDER_100:
//etc
}
but this is serious overkill for what youre trying to do. i'd use that if this division is also useful elsewhere in your code.
Switch case function must have an exact number in case. For example:
case 0:
case 1:
You're trying to use case from some value to some value and it's not implemented that way in Java. For your problem, you must use if-else statement since it's impossible to do it with switch case. Hope it helped.
Look the problem is very basic..
In a switch statement it allows only the following datatypes and wrapper classes
Byte,short,char,int,Byte,Short,Character,Integer,enum,String..
If you are passing anything other than that will give you an error.
In your case the condition which you are evaluating will give you result which is a Boolean value.
NavigableMap.seilingEntry() may be a good solution in many cases,
but in other cases the following may be clearer:
double getPrice(int copies){
return copies>1000 ? 0.25
: copies>750 ? 0.26
: copies>500 ? 0.27
: copies>100 ? 0.28
: copies>0 ? 0.30
: 0; // or check this condition first, throwing an exception
}
I am trying to generate a digit to execute switch statement but it is not generating proper result. But when the IF block is removed it works properly. What is the problem in the code?
import static java.lang.Character.isDigit;
public class TrySwitch
{
enum WashChoise {Cotton, Wool, Linen, Synthetic }
public static void main(String[]args)
{
WashChoise Wash = WashChoise.Cotton;
int Clothes = 1;
Clothes = (int) (128.0 * Math.random());
if(isDigit(Clothes))
{
switch (Clothes)
{
case 1:
System.out.println("Washing Shirt");
Wash = WashChoise.Cotton;
break;
case 2:
System.out.println("Washing Sweaters");
Wash = WashChoise.Wool;
break;
case 3:
System.out.println("Socks ");
Wash = WashChoise.Linen;
break;
case 4:
System.out.println("washing Paints");
Wash = WashChoise.Synthetic;
break;
}
switch(Wash)
{
case Wool:
System.out.println("Temprature is 120' C "+Clothes);
break;
case Cotton:
System.out.println("Temprature is 170' C "+Clothes);
break;
case Synthetic:
System.out.println("Temprature is 130' C "+Clothes);
break;
case Linen:
System.out.println("Temprature is 180' C "+Clothes);
break;
}
}
else{
System.out.println("Upps! we don't have a digit, we have :"+Clothes );
}
}
}
You are not using isDigit() properly, it takes a char as an argument, not an int, see this link: http://www.tutorialspoint.com/java/character_isdigit.htm
The trick is that the isDigit method is meant for characters and detecting whether they represent a number. For example isDigit(8) == false because 8 maps to backspace in ASCII, but isDigit('8') == true since '8' is really 56 in ASCII.
What you might want to do is remove the if altogether and change your random generation to always produce a number between 1 and 4. This can be done as follows:
Clothes = ((int) (128.0 * Math.random())) % 4 + 1;
The % 4 will make sure the value is always between 0 and 3, and the + 1 shifts the range to 1 to 4.
You can also use the Random class included with java:
import java.util.Random;
...
Clothes = new Random().nextInt(4) + 1
Once again the + 1 shifts the range to be 1 to 4 inclusive.
isDigit() essentially tests for an ascii value in the range 48-57, ie, characters which are digits. Chances are, that's not what Clothes is.
http://www.asciitable.com/
I'm sure there are better examples than mine:)
Let's say that it's snowing and the users can earn points for each snowflake, but they have to do it fast to no get stuck in the snow, so this is my ex:
class apples{
public static void main(String args[]){
int points;
points = 1;
switch (points){
case 1:
System.out.println("32");
break;
case 2:
System.out.println("Almost half");
break;
case 3:
System.out.println("You're near");
break;
case 4:
System.out.println("Congratulations., You got 100 points");
default:
System.out.println("Want to start again?");
break;
}
}
}
The switch statement has been miss-used for a long time.
The original idea was to have an entry point system; a goto-like statement which worked like this :
If my value is 1; goto 1;
Else If my value is 2; goto 2;
Else If my value is 3; goto 3;
Else If goto default;
label 1 : ...;
label 2 : ...;
label 3 : ...;
label default : ...;
And people started to like this system and decided that it would be better than having a lot of if/else statements. So they used a little trick, the break; And now people really enjoy the switch as a replacement of the if/else by breaking every case of the switch.
To have a really good example of the original switch statement, you should have something like this:
public void printDaysLeftUntilNextMonday(){
switch(dayOfWeek){
case 1 :
System.out.println("Monday");
case 2 :
System.out.println("Tuesday");
case 3 :
System.out.println("Wednesday");
case 4 :
System.out.println("Thursday");
case 5 :
System.out.println("Friday");
case 6 :
System.out.println("Saturday");
case 7 :
System.out.println("Sunday");
}
}
I had a real use case on day (rare thing if you don't abuse of break; in switch) it was in a Hangman.
public void printHangman(){
switch(triesLeft){
case 1 :
printLeftLeg();
case 2 :
printRightLeg();
case 3 :
printLeftArm();
case 4 :
printRightArm();
case 5 :
printBody();
case 6 :
printHead();
}
}
If you want to have more flexibility than a HashMap (not that there's anything wrong with the solution), you can go with a chain of responsibility :
class PointScore {
private PointScore next;
private int points;
private String msg;
public PointScore(int points, String msg) {
this.points = points;
this.msg = msg;
this.next = null;
}
public PointScore setNext(PointScore next) {
this.next = next;
return next;
}
public boolean checkScore(int points) {
if (this.points == points) {
System.out.println(this.msg);
return true;
} else if (null != next) {
return next.checkScore(points);
} else {
return false;
}
}
}
Then your main entry point :
class Apples {
public static void main(String...args) {
int points;
points = 1;
// set first condition (highest priority first)
PointScore scores = new PointScore(4, "Congratulations., You got 100 points");
// set next chain members in order or priority (highest to lowest)
scores.setNext(new PointScore(3, "You're near"))
.setNext(new PointScore(2, "Almost half"))
.setNext(new PointScore(1, "32"));
if (!scores.checkScore(points)) {
System.out.println("Want to start again?");
}
}
}
This doesn't look much, but the checkScore method can perform other checks; for example, you could setup a range of values instead of a single points integer, etc.
Use a dictionary or a hashmap to map the number of points to the string.
I find switch statements make most sense when the range of a variable is bounded. So for example the days-of-the-week example given here is fine, and the one with the enum is even better.
Bit of a no-brainer, but wikipedia has an excellent page with the history, advantages and disadvantages of the switch statement, as well as a host of examples in different languages.
Okay here we go. At work we often use enum types, simple example:
public enum Colors {
RED,
GREEN,
BLUE,
YELLOW,
VIOLET,
BROWN,
ORANGE; // more to come
}
so we can switch over these literal constants:
public String colorToMood(final Colors color) {
String mood = "everything the same to me";
switch (color) {
case RED:
mood = "excited";
break;
case YELLOW:
mood = "I like the sun";
break;
case GREEN:
mood = "forests are nice";
break;
case BLUE:
mood = "I feel free like a bird in the sky";
break;
// fill in your code here for VIOLET, BROWN, ORANGE
// otherwise they get handled by the default clause
default:
mood = "I don't know your color";
break;
}
return mood;
}
Maybe you now get a better idea what the benefits of a switch in conjunction with enums are. You can even define a constructor for your enum constants, but that gets too advanced...