I'm trying to create a switch statement that takes the month in as an integer, and based on that integer, I'd like to output a month name. For some reason that I don't know, the case '10' gives me an Invalid character constant error message. Does anyone know why this is happening and how I can solve this? Thanks, the code is below:
switch (month) {
case '1': System.out.println("January");
break;
case '2': System.out.println("February");
break;
case '3': System.out.println("March");
break;
case '4': System.out.println("April");
break;
case '5': System.out.println("May");
break;
case '6': System.out.println("June");
break;
case '7': System.out.println("July");
break;
case '8': System.out.println("August");
break;
case '9': System.out.println("September");
break;
case '10': System.out.println("October");
break;
case '11': System.out.println("November");
break;
case '12': System.out.println("December");
break;
}
After answer:
switch (month) {
case "1": System.out.println("January");
break;
case "2": System.out.println("February");
break;
case "3": System.out.println("March");
break;
case "4": System.out.println("April");
break;
case "5": System.out.println("May");
break;
case "6": System.out.println("June");
break;
case "7": System.out.println("July");
break;
case "8": System.out.println("August");
break;
case "9": System.out.println("September");
break;
case "10": System.out.println("October");
break;
case "11": System.out.println("November");
break;
case "12": System.out.println("December");
break;
}
after more answers:
switch (month) {
case 1: System.out.println("January");
break;
case 2: System.out.println("February");
break;
case 3: System.out.println("March");
break;
case 4: System.out.println("April");
break;
case 5: System.out.println("May");
break;
case 6: System.out.println("June");
break;
case 7: System.out.println("July");
break;
case 8: System.out.println("August");
break;
case 9: System.out.println("September");
break;
case 10: System.out.println("October");
break;
case 11: System.out.println("November");
break;
case 12: System.out.println("December");
break;
}
'10' has two characters, i.e. a '1' and a '0'
Why don't you just use int instead of char for you switch statement variable...
int month = // ... however you get your month
switch(month) {
case 1: // ...
case 2: // ...
case 3: // ...
// ...
}
In Java `` denotes a character whereas "" denotes a string. 10 is not a character in Java but two characters therefore you cannot place it there.
In Java 7 you can do a switch on Strings so you'd have to change all your `` to "" and month to a String like this:
switch(month) {
case "1": // stuff
/* rest */
}
Or drop the `` altogether and switch on int:
switch(month) {
case 1: // stuff
/* rest */
}
As said by others '10' has 2 characters . Why don't you use integers instead :
int month;
switch(month){
case 1:
break;
.
.
.
}
From java 1.7 Strings are also allowed in switch statements so you can also write :
String month = // i/p
switch(month){
case "1" :
break;
.
.
.
.
.
}
You are having 2 characters after the 9
e.g. 10, 11, 12
So that can't be consider as a single char. That is why you are getting the error.
If you are using Java version 1.7 or above you can use string instead of char. But I think the best way is to cast month variable to a int and have int cases
//first cast month to a int
switch (month) {
case 1: System.out.println("January");
break;
case 2: System.out.println("February");
break;
......
case 10: System.out.println("October");
break;
case 11: System.out.println("November");
break;
case 12: System.out.println("December");
break;
}
If you make month as integer, then remove single quotes and it will work
else make month as string it will work.
Related
**About the code: I am just making a simple code using a switch statement. All the switch cases work fine except the double-digit cases. I get an error saying :
year.java:37: error: unclosed character literal
case '10'
year.java:40: error: unclosed character literal
case '11':year.java:43: error: unclosed character literal
case '12'
Code :
import java.util.Scanner;
public class year {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
char year;
System.out.println("Enter the number of the month ");
year = input.next().charAt(0);
switch(year){
case '1':
System.out.println("January");
break;
case '2':
System.out.println("Febraury");
break;
case '3':
System.out.println("March");
break;
case '4':
System.out.println("April");
break;
case '5':
System.out.println("May");
break;
case '6':
System.out.println("June ");
break;
case '7':
System.out.println("July");
break;
case '8':
System.out.println("August ");
break;
case '9':
System.out.println("September ");
break;
case '10':
System.out.println("October");
break;
case '11':
System.out.println("November");
break;
case '12'
System.out.println("December");
break;
default:
System.out.println("Invalid");
}
input.close();
}
}
I tried doing a few changes here and there but couldn't understand them and thus could not do so.
Your variable year is a char. A char can only be a single character.
Therefore when you try and do '11' or '12' you run into issues as these "chars" consist of more than one character.
The quick solution here would be to use a String instead of char, using input.next() without the .charAt(0). Then you would need to change your case statements to use double quotes instead of single quotes.
Alternatively, you could do Integer.parseInt(input.next()) and then switch on an int instead, as #Tom has suggested.
First of all, there is a Syntax error in case '12' it should be case '12':
(Also the code indention is bad. Poor indentation make it hard for debugging)
I suggest you convert this code to a String based one. Please check the complete example below.
Char can get one character only and char year; cause a bug, because in input values like 10, 11, 12 it won't work as expected
import java.util.Scanner;
public class year {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
String year;
System.out.println("Enter the number of the month ");
year = input.nextLine();
switch(year){
case "1":
System.out.println("January");
break;
case "2":
System.out.println("Febraury");
break;
case "3":
System.out.println("March");
break;
case "4":
System.out.println("April");
break;
case "5":
System.out.println("May");
break;
case "6":
System.out.println("June ");
break;
case "7":
System.out.println("July");
break;
case "8":
System.out.println("August ");
break;
case "9":
System.out.println("September ");
break;
case "10":
System.out.println("October");
break;
case "11":
System.out.println("November");
break;
case "12":
System.out.println("December");
break;
default:
System.out.println("Invalid");
}
input.close();
}
}
I'm creating a code that will output a number based on the input letter. My code is stuck was stuck on a loop of doing character 0 repeatedly. Friend said that char Check = userInput.charAt(numTelephone); would fix it. When I placed that into my code I recieved the error: error: char cannot be dereferenced char Check = userInput.charAt(numTelephone);
import java.util.Scanner;
public class PhoneWords {
public static void main(String []args){
Scanner scnr = new Scanner(System.in);
int numTelephone;
char userInput;
userInput = scnr.next().charAt(0);
System.out.println("Enter a telephone number using letters (EXIT to quit): ");
System.out.println("The corresponding telephone number is: ");
if ((userInput >= 'A') || (userInput <= 'Z') || (userInput >= 'a') || (userInput <= 'z')){
for (numTelephone = 0; numTelephone < 7; numTelephone++){
char Check = userInput.charAt(numTelephone);
if (numTelephone == 3){
System.out.print("-");
}
switch (userInput) {
case 'A':
case 'a':
case 'B':
case 'b':
case 'C':
case 'c':
System.out.print("2");
break;
case 'D':
case 'd':
case 'E':
case 'e':
case 'F':
case 'f':
System.out.print("3");
break;
case 'G':
case 'g':
case 'H':
case 'h':
case 'I':
case 'i':
System.out.print("4");
break;
case 'J':
case 'j':
case 'K':
case 'k':
case 'L':
case 'l':
System.out.print("5");
break;
case 'M':
case 'm':
case 'N':
case 'n':
case 'O':
case 'o':
System.out.print("6");
break;
case 'P':
case 'p':
case 'Q':
case 'q':
case 'R':
case 'r':
case 'S':
case 's':
System.out.print("7");
break;
case 'T':
case 't':
case 'U':
case 'u':
case 'V':
case 'v':
System.out.print("8");
break;
case 'W':
case 'w':
case 'X':
case 'x':
case 'Y':
case 'y':
case 'Z':
case 'z':
System.out.print("9");
break;
default:
break;
}
}
}
}
}
The type char is primitive -- not an object -- so it cannot be dereferenced
Dereferencing is the process of accessing the value referred to by a reference. Since a char is already a value (not a reference), it can not be dereferenced.
so get the char from the given input like:
char userInput = scnr.nextLine().charAt(0);
And comment this line which is suggested by your friend which is not used any where:
//char Check = userInput.charAt(numTelephone);
So I am writing code that will take a character and return its alpha-numeric keypad equivalent as a character.
The problem is, I am getting a question mark in a box as a return. I have checked that the input is correct. For example, with a char 'h' input, i should get a char '4' return. Hoping someone is able to spot my error.
Code is below:
public char getDigit(char letter) throws Exception{
switch (letter) {
case 'a': case 'b': case 'c': case '2':
return 2;
case 'd': case 'e': case 'f': case '3':
return 3;
case 'g': case 'h': case 'i': case '4':
return 4;
case 'j': case 'k': case 'l': case '5':
return 5;
case 'm': case 'n': case 'o': case '6':
return 6;
case 'p': case 'q': case 'r': case 's': case '7':
return 7;
case 't': case 'u': case 'v': case '8':
return 8;
case 'w': case 'x': case 'y': case 'z': case '9':
return 9;
default:
throw new IllegalArgumentException("Must be a letter or number on the Alpha-Numeric Keypad.");
}
}
The return type of your method is char.
Now take your switch statement. You return char values in the range from 2 to 9. Now look at an ASCII table.
Surprise: these chars are all "unprintable" control characters. Thus your console gives you "?" when you print them!
If you want '4', your code has to return '4', not 4! Or 52, because that entry in the ASCII table represents '4'.
You are not getting proper output because you are using char as a return type of getDigit(..) function. You should use int as a return type instead of char as in switch case you are comparing with characters and returning digit values So replace your code with the following code, this will work:
public int getDigit(char letter) throws Exception{
switch (letter) {
case 'a': case 'b': case 'c': case '2':
return 2;
case 'd': case 'e': case 'f': case '3':
return 3;
case 'g': case 'h': case 'i': case '4':
return 4;
case 'j': case 'k': case 'l': case '5':
return 5;
case 'm': case 'n': case 'o': case '6':
return 6;
case 'p': case 'q': case 'r': case 's': case '7':
return 7;
case 't': case 'u': case 'v': case '8':
return 8;
case 'w': case 'x': case 'y': case 'z': case '9':
return 9;
default:
throw new IllegalArgumentException("Must be a letter or number on the Alpha-Numeric Keypad.");
}
}
I very new beginner in Java
Please help!
I need to declare "chk" in order to let switch know where to go.
How can I declare in something like this in order to let the switch know I need to check all 4 output and display them accordingly, not just output 1:
CheckBox chk = (CheckBox) findViewById(R.id.chk1);
switch (chk.getId()) {
case R.id.chk1:
findViewById(R.id.output1).setVisibility(visible);
break;
case R.id.chk2:
findViewById(R.id.output2).setVisibility(visible);
break;
case R.id.chk3:
findViewById(R.id.output3).setVisibility(visible);
break;
case R.id.chk4:
findViewById(R.id.output4).setVisibility(visible);
break;
}
The switch Statement
Unlike if-then and if-then-else statements, the switch statement can have a number of possible execution paths. A switch works with the byte, short, char, and int primitive data types. It also works with enumerated types (discussed in Enum Types), the String class, and a few special classes that wrap certain primitive types: Character, Byte, Short, and Integer (discussed in Numbers and Strings).
The following code example, SwitchDemo, declares an int named month whose value represents a month. The code displays the name of the month, based on the value of month, using the switch statement.
public class SwitchDemo {
public static void main(String[] args) {
int month = 8;
String monthString;
switch (month) {
case 1: monthString = "January";
break;
case 2: monthString = "February";
break;
case 3: monthString = "March";
break;
case 4: monthString = "April";
break;
case 5: monthString = "May";
break;
case 6: monthString = "June";
break;
case 7: monthString = "July";
break;
case 8: monthString = "August";
break;
case 9: monthString = "September";
break;
case 10: monthString = "October";
break;
case 11: monthString = "November";
break;
case 12: monthString = "December";
break;
default: monthString = "Invalid month";
break;
}
System.out.println(monthString);
}
}
import java.util.Scanner;
public class ConvertLetterToNumber {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.println("Enter one letter");
String str = input.next();
char ch = str.charAt(0);
switch (ch){
case 'A': case 'a': case 'B': case 'b': case 'C': case 'c':
System.out.println("the number is 2");
break;
case 'D': case 'd': case 'E': case 'e': case 'F': case 'f':
System.out.println("the number is 3");
break;
case 'G': case 'g': case 'H': case 'h': case 'I': case 'i':
System.out.println("the number is 4");
break;
case 'J': case 'j': case 'K': case 'k': case 'L': case 'l':
System.out.println("the number is 5");
break;
case 'M': case 'm': case 'N': case 'n': case 'O': case 'o':
System.out.println("the number is 6");
break;
case 'P':case 'p': case 'Q': case 'q': case 'R': case 'r': case 'S': case's':
System.out.println("the number is 7");
break;
case 'T':case 't':case 'U':case'u':case'V':case 'v':
System.out.println("the number is 8");
break;
case 'W':case 'w':case 'X': case 'x': case 'Y':case'y':case 'Z':case 'z':
System.out.println("the number is 9");
break;
default :System.out.println("Error:invalid input");
System.exit(1);
}
}
}
the problem is if I enter two or more letters at one time (for example "ab" the answer will be "2", but what I want is "Invalid input". How can I add this instruction to ask user to enter only one letter?
You could check the str length before your switch, and return like so:
if (str.length > 1){
return;
}