I have this code with the switch statement which I got from this post, and it works absolutely fine:
String getOrdinal(final int day) {
if (day >= 11 && day <= 13) {
return "th";
}
switch (day % 10) {
case 1: return "st";
case 2: return "nd";
case 3: return "rd";
default: return "th";
}
}
But if I change it to something like the following, it breaks, as all the cases besides case 1 gets executed:
static String getOrdinal(final int day) {
StringBuilder ordinalBuilder = new StringBuilder();
ordinalBuilder.append("<sup>");
if (day >= 11 && day <= 13) {
ordinalBuilder.append("th") ;
}
switch (day % 10) {
case 1: ordinalBuilder.append("st");
case 2: ordinalBuilder.append("nd");
case 3: ordinalBuilder.append("rd");
default: ordinalBuilder.append("th");
}
ordinalBuilder.append("</sup>");
return ordinalBuilder.toString();
}
This prints 2<sup>ndrdth</sup> when I pass in 2. I tried changing the builder to buffer but I got the same response... Could this be a bug or am I making some mistake?
It's a bug in your code. You forgot to put in a break after each case:
switch (day % 10) {
case 1: ordinalBuilder.append("st"); break;
case 2: ordinalBuilder.append("nd"); break;
case 3: ordinalBuilder.append("rd"); break;
default: ordinalBuilder.append("th"); break;
}
I don't see any bug here, at least not in the way the language is working. The behavior of a switch statement, by design, is that it will start executing statements at the case label which matches the argument, and then continue until the end of the block. So
switch (x) {
case 1:
// do thing 1
case 2:
// do thing 2
case 3:
// do thing 3
default:
// do nothing
}
will do both things 2 and 3 if x is 2, and will do things 1, 2, and 3 if x is 1.
To get the behavior you're probably looking for, end each case with a break:
switch (x) {
case 1:
// do thing 1
break;
case 2:
// do thing 2
break;
case 3:
// do thing 3
break;
default:
// do nothing
break;
}
(strictly speaking the break at the very end is unnecessary, but I often put it in out of habit).
The reason you didn't have this problem in the first code example is that return is like a super-break: it has the same effect as break, namely ending execution within the switch block, but it also ends execution of the whole method.
you need to add a 'break' statement in every switch case.
It was worked previously because you made a return from method...
A "break;" statement separates the cases from one another so in order to execute the statements in a specific case just break the case as soon as it comes to an end.
If you don't use break the compiler thinks that it can continue execution of all the cases up to the end of the program.
The first version returns before continuing on in the case statement. The second version needs a break; statement to get the same behavior.
Luckily with the introduction of switch statements on Java 12 which also introduced
"arrow case" labels that eliminate the need for break statements to
prevent fall through (source).
Therefore the modern version of your code looks like the following:
String getOrdinal(final int day) {
if (day >= 11 && day <= 13) {
return "th";
}
return switch (day % 10) {
case 1 -> "st";
case 2 -> "nd";
case 3 -> "rd";
default -> "th";
};
}
I see this question is over 8 years old, but this answer should help anyone landing on this page.
Firstly lets's understand how switch cases work. In C, C++, Java, JavaScript, and PHP while executing switch statements all the cases following the satisfactory case are executed, unlike in Go where only selected case is executed.
For example:
public class Main
{
public static void main(String[] args) {
int day = 11;
switch (day % 10) {
case 1: System.out.println("st");
case 2: System.out.println("nd");
case 3: System.out.println("rd");
default: System.out.println("th");
}
}
}
Currently, day value is set to 11 and hence very first case satisfy the condition, and hence all below cases would be executed. The output should look like the one below:
st
nd
rd
th
Now let's change day value to 13 resulting in the third case to satisfy the condition and hence below output is obtained:
rd
th
Hence if you want to break the code after first satisfactory case is found then put break; condition in the end. In the code mentioned in the question return; does the job of breaking the code.
Also, most of the novice java programmers believe that SWITCH statements are syntactical sugar to IF statements wherein programmers don't have to repetitively mention conditions. But that's not the case as IF's are meant to exit after the execution of satisfactory condition while SWITCH still continues execution.
Switch cases can be utilized to achieve the purpose like one mentioned in below example:
wherein
for Grade A "Excellent!" should be printed
for Grade B and C "Well done" should be printed
for Grade D "You passed \n Try hard next time" should be printed
for Grade F "Try hard next time" should be printed
and if not a valid case i.e grade is found than "Invalid Grade" should be printed.
public class Test {
public static void main(String args[]) {
// char grade = args[0].charAt(0);
char grade = 'C';
switch(grade) {
case 'A' :
System.out.println("Excellent!");
break;
case 'B' :
case 'C' :
System.out.println("Well done");
break;
case 'D' :
System.out.println("You passed");
case 'F' :
System.out.println("Try hard next time");
break;
default :
System.out.println("Invalid grade");
}
System.out.println("Your grade is " + grade);
}
}
Add a break statement at the end of the every line in each case or just use the return statement.
Related
Hi please in a switch case program that I am developing, I am using a do..while loop to handle the case when a user enters a value that does not meet the condition but got stuck with what I should put in the "while" brackets as an error is shown on the "while" line..
package assignment;
import java.util.*;
public class Assignment {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("1)Monday\n2)Tuesday\n3)Wednesday\n4)Thursday\n5)Friday\n6)Saturday\n7)Sunday");
System.out.println("");
int day = input.nextInt();
System.out.println(" ");
do {
switch (day) {
case 1:
System.out.println("Monday");
break;
case 2:
System.out.println("Tuesday");
break;
case 3:
System.out.println("Wednesday");
break;
case 4:
System.out.println("Thursday");
break;
case 5:
System.out.println("Friday");
break;
case 6:
System.out.println("Saturday");
break;
case 7:
System.out.println("Sunday");
break;
default:
System.out.println("Oh oh, that's not an accepted number, kindly try again");
break;
}
for (int clear = 0; clear < 1000; clear++) {
System.out.println("\b");
}
} while (!(day.equals("1") || day.equals("2") || day.equals("3") || day.equals("4") || day.equals("5") || day.equals("6") || day.equals("7")));
}
}
Instead of checking day as a String, simply check it as an integer which it already is. No need to allocate extra memory when creating a new String to check with an integer.
When you begin your while loop, it seems that there is no way to check for new input. How would you be able to get new input EACH time in your loop?
There is no reliable way to clear your console cross platform as depending on the IDE you are using or which terminal UNIX or PowerShell or CMD. Take a look at this answer Java: Clear the console
Since this seems like a homework assignment, I suggest that you think about how your while loop conditions could be simplified.
Hint: Is there any way to check a range of numbers? What if you had to check 1000 different numbers, would you check each number with OR conditions?
I'm new to Java and am learning switch statements. However, the wrong case (case "two") seems to be matched. I suspect that it's because of the lack of break; after case "one", but can someone please explain to me the logic behind Java switch statements? Why is case "two" matched at all when the values don't even match?
Here is my code:
String a = "one";
switch(a) {
case "one": System.out.println("a is one");
case "two": System.out.println("a is two");
default: System.out.println("numbers");
}
I expected output:
a is one
numbers
But got:
a is one
a is two
numbers
The case statement is evaluated from top to bottom, when it finds a match it will enter at that point and continue downwards until a break is found (or it gets to the bottom without finding a match). You cannot drop into "one", skip over "two" and re-enter a default.
Default is used when none of the other cases above it match
You need break statements
String a = "one";
switch(a) {
case "one": System.out.println("a is one"); break;
case "two": System.out.println("a is two"); break;
default: //
}
System.out.println("numbers")
Then maybe print the numbers afterward
Each break statement terminates the enclosing switch statement. Control flow continues with the first statement following the switch block. The break statements are necessary because without them, statements in switch blocks fall through: All statements after the matching case label are executed in sequence, regardless of the expression of subsequent case labels, until a break statement is encountered.
If all the cases has been checked and not passed then default case will be executed. Thus in your case the code should be like this.
String a = "one";
switch(a) {
case "one":
System.out.println("a is one");
break;
case "two":
System.out.println("a is two");
break
default:
System.out.println("None of the cases matched ");
}
System.out.println("numbers");
In switch statement, the value of the expression is compared with each of the literal values in the case statements. If a match is found l, the code sequence following the case is executed. However, the default statement is optional.
The break statement is used inside the switch to terminate a statement sequence.
When a break statement is encountered, execution branches to the first of code that follows the entireswitch statement.
This has the effect of jumping out of the switch.
If you omit the break execution will continue on into the next case.
I am trying to make a switch that will step through the code like in Javascript by adding "jedi++" at the end but it won't let me do that any suggestions on how I can accomplish that? Here is a snippet of the code.
switch(jedi){
case 1:
while(!input.equalsIgnoreCase("guardian") && !input.equalsIgnoreCase("sentinel") && !input.equalsIgnoreCase("consular")){
System.out.println("Please enter the path followed by this Jedi.");
System.out.println("(Guardian, Sentinel or Consular)");
}
registrant.setPath(input);
break;
case 2:
while(!input.equalsIgnoreCase("master") && !input.equalsIgnoreCase("knight") && !input.equalsIgnoreCase("padawan")
&& !input.equalsIgnoreCase("youngling")){
System.out.println("Please enter the Jedi's Rank.");
System.out.println("(Master, Knight, Padawan, Youngling)");
input = keyboard.nextLine();
}
registrant.setRank(input);
break;
jedi++;
}
Do you want to jedi++ in all the cases or just in case 2?
If it's just for case 2, you could do
case 2:
....
jedi++;
break;
case 3:
....
if it's for all the cases, you could do jedi++ after the switch block.
Statements can exist only within the case. since jedi++ is not part of case, its throwing error. Putting the increment statement under required case statement will solve the issue.
I was answering a Java test and come across the question:
Which of the following statements is true?
A. In an assert statement, the expression after the colon ( : ) can
be any Java expression.
B. If a switch block has no default, adding an assert default is considered appropriate.
C. In an assert statement, if the expression after the colon ( : ) does not have a
value, the assert's error message will be empty.
D. It is appropriate to handle assertion failures using a catch clause.
The right answer is B. To be honest, I answered that question by excluding another obviously wrong cases, but I can't get the point of that question actually. Could anyone explain why it is true? Where can it be helpful?
I guess it means you should protect yourself from missing a switch case.
Say you have an enum Color {red, green} and this switch in the code:
switch(color) {
case red:
doSomethingRed();
break;
case green:
doSomethingGreen();
break;
}
If in the future you add a new color blue, you can forget to add a case for it in the switch.
Adding failing assert to the default case will throw AssertionError and you will discover your mistake .
switch(color) {
case red:
doSomethingRed();
break;
case green:
doSomethingGreen();
break;
default:
assert false : "Oops! Unknown color"
}
This depends on the case but the way I see it
// Consider expecting only 1,2 or 3 as switch case
switch(x)
{
case 1:
// operations
break;
case 2:
// operations
break;
case 3:
// operations
break;
default: assert false : "Input should be between 1-3";
}
Might be convenient as any other input you might receive can be perceived as a faulty input.
Using assert false in switch block's default is applicable in the public method context e.g.
public void methA(int x) throws Exception {
if(x!=1 && x!=2 && x!=3)
throw new IllegalArgumentException("from Exception: x should be between 1,2 and 3");
switch(x)
{
case 1: doSomething(); break;
case 2: doSomething(); break;
case 3: doSomething(); break;
default: assert false : "from default: x should be between 1,2 and 3";
}
}
If the switch block is used in a public method, then checking the value of the argument x is already handled by an exception before the switch statement.
So, even when you use the assert false in default, that code is never reachable, since the assumption that x is 1,2 or 3 is always true. If not true, it is already handled by the IllegalArgumentException before the switch default. So basically, the assumption that switch-default will never be reached is always true. Hence it is appropriate in the context of public method.
This question already has answers here:
Is "else if" faster than "switch() case"? [duplicate]
(14 answers)
Closed 9 years ago.
I need to check a small piece of logic and would highly appreciate if someone can give me some valuable input.
I have two ways of checking my logic and want to know which is more efficient.
1st way:
if(url.equalsIgnoreCase("1")){
url = "aaa";
}
else if(url.equalsIgnoreCase("2")){
url = "bbb";
}
else if(url.equalsIgnoreCase("3")){
url = "ccc";
}
else if(url.equalsIgnoreCase("4")){
url = "ddd";
}
else if(url.equalsIgnoreCase("5")){
url = "eee";
}
else if(url.equalsIgnoreCase("6")){
url = "fff";
}
2nd Way:
int temp = Integer.parseInt(url);
switch (temp) {
case 1:
url = "aaa";
break;
case 2:
url = "bbb";
break;
case 3:
url = "ccc";
break;
case 4:
url = "ddd";
break;
case 5:
url = "eee";
break;
case 6:
url = "fff";
break;
}
Please let me know which is more efficient. Is it bad to use Integer.parseInt(string)?
If your values really are 1-6, the clearest and most efficient way is using an array :
String[] URLS = {...};
url = URLS[Integer.parseInt(url) - 1];
Please let me know which is more efficient.
a switch statement is more efficient is your case
Is it bad to use Integer.parseInt(string)?
No. it's fine. but when you're using java7 you can use String-constants values in your switch cases but not on Android.
Asside from the efficiency: switch looks cleaner in most cases.
In terms of efficiency check this: Case vs If Else If: Which is more efficient?, but Way 2 looks to be a more clean and readable code.
As a general rule, the switch statement produces more efficient bytecode. With Java 7, switch statements with String was introduced, so you don't need to cast it.
In this case, switch is more efficient.
In fact, If you are using Java7, you may directly use string case rather than using Integer.parseInt().
It is not bad using parseInt but it will throw an exception if the string is not an integer.
otherwise, and I think you can see this for yourself, the switch/case is much more readible.
if your if construct would have a final else catching all other cases (including non numeric strings)
then you can do, assuming your ints are always positive
int temp = -1;
try {
temp = Integer.parseInt(str);
} catch (NumberFormatException ex) {
// ignore exception and use -1 as original value for default case
}
Readability and debugability (is that even a word?) are rather subjective but some people (including me) find the switch statement to be more clear. However, in many cases a compiler has a better chance of generating faster code using a switch compared to the if else construct.
The switch statement is faster for the following two reasons.
The switch statement is generally faster than if-else-if construct because the control is directly transferred to the respective case. While in the cases of if-else-if, the all the checks are going to be performed to reach the first matching condition. For example, if you assign temp = 6 the switch statement will execute the respective block directly. The if-else-if construct will iterate through all the conditions.
Calling the equalsIgnoreCase() is more costly than performing the equality check that happens at the background of the case matching.
for such a long list is a switch statement definitely the better choice. The longer the junction is if the better cut off a switch in comparison
Efficiency depends on the matching condition in both cases.Please conform your answer here.
I think an alternative approach would be to use a pre initialized map. It should have the (string)numbers as the key and the url results as value. Then you can simply do
url = map.get(Integer.parseInt(url));
This is probably even a much cleaner version then the long switch statement.
The switch has more features than the if else, because you can fall through cases.
See for details: http://docs.oracle.com/javase/tutorial/java/nutsandbolts/switch.html
class SwitchDemo2 {
public static void main(String[] args) {
int month = 2;
int year = 2000;
int numDays = 0;
switch (month) {
case 1: case 3: case 5:
case 7: case 8: case 10:
case 12:
numDays = 31;
break;
case 4: case 6:
case 9: case 11:
numDays = 30;
break;
case 2:
if (((year % 4 == 0) &&
!(year % 100 == 0))
|| (year % 400 == 0))
numDays = 29;
else
numDays = 28;
break;
default:
System.out.println("Invalid month.");
break;
}
System.out.println("Number of Days = "
+ numDays);
}
}
will output
Number of Days = 29
So it also depends on your implementation requirements which one you use.