Program skips "If" code and goes straight to "Else"

[Logik22]

My program runs correctly except for the fact that it seems to skip the "If" portion of the code and go directly to "Else" even when I hard code the user response in to be the correct response for the "If" portion.

//Imports package to enable scanner to read user input
import java.util.Scanner;

//'TempConverter' Class
public class TempConverter
{

//'main' method
public static void main(String[] args)
{
//Calls the 'convert' class so the program can gather input, perform calculations, and output data.
convert();

//Calls 'exit' class to prompt user to exit or restart.
exit();

}



public static void convert()
{

//Creates variable for user input. User input should be 'C' or 'F'.
String TempScale;
//Creates variable for user inputted temperature. This is the number that will be converted.
String RawTemp;
//Variable to hold RawTemp conversion from String to Double so the calculation may be performed
Double Temp;
//Variable for converted temperature to be output to screen
Double CTemp;

//Output to prompt user for input
System.out.println("Please input 'C' to convert 'Fahrenheit to Celsius' or input 'F' to convert 'Celsius to Fahrenheit'.");

//Scanner to read user input
Scanner ScaleInput = new Scanner(System.in);

//Assigns 'TempScale' to user input
TempScale = ScaleInput.nextLine();

//Verifies user input valid answer
if(TempScale != "F" || TempScale != "f" || TempScale != "C" || TempScale != "c"){
	System.out.println("Please input a valid answer. Valid answers are F, f, C,  c");
	convert();
	
//Runs conversion
} else {
	
if(TempScale == "F" || TempScale == "f"){
	
//Confirms user input
System.out.println("You have select to convert from Celsius to Fahrenheit.");
//Asks user for temperature
System.out.println("Please input the Celsious temperature you want converted.");
//Reads input
Scanner TempInput = new Scanner(System.in);
//Assigns input to 'RawTemp'
RawTemp = TempInput.nextLine();
//Converts String 'RawTemp' to Double 'Temp'
Temp = Double.parseDouble(RawTemp);
//Converts to Fahrenheit
CTemp = (Temp*1.8) + 32;
//Outputs temperature in both measurements
System.out.println("Celcius: " + Temp);
System.out.println("Fahrenheit: " + CTemp);

} else {
	
	//Confirms user input
	System.out.println("You have select to convert from Fahrenheit to Celsius.");
	
	//Asks user for temperature
	System.out.println("Please input the Fahrenheit temperature you want converted.");
	
	//Reads input
	Scanner TempInput = new Scanner(System.in);
	
	//Assigns input to 'RawTemp'
	RawTemp = TempInput.nextLine();
	
	//Converts String 'RawTemp' to Double 'Temp'
	Temp = Double.parseDouble(RawTemp);
	
	//Converts to Fahrenheit
	CTemp = (Temp-32)/1.8;
	
	//Outputs temperature in both measurements
	System.out.println("Fahrenheit: " + Temp);
	System.out.println("Celsius: " + CTemp);	
}

}
}

public static void exit()
{
//Variable prompting user to exit
String ExitReply;
	
System.out.println("If you would like to exit the program please type 'exit', otherwise type 'retry' to restart the program.");

//Scanner to read user input
Scanner ExitInput = new Scanner(System.in);

//Assigns 'ExitReply' to user input
ExitReply = ExitInput.nextLine();

//Test output
System.out.println(ExitReply + " ECHO");

//Verifies user put in valid answer
if(ExitReply == "exit" || ExitReply == "Exit" || ExitReply == "Retry" || ExitReply == "retry"){
	
	//If-else statement to Retry or Exit program
		if(ExitReply == "Retry" || ExitReply == "retry"){
			//Test output
			System.out.println("test");
			//Restarts program
			convert();
			exit();
	} else {
		
		//Test output
		System.out.println("test2");
		
		//Closes program
		System.exit(0);
	} 

}
else{
	//Prompts user to put in valid response
	System.out.println("Please input either 'exit' or 'retry'.");
	exit();
}
}


}

[eRaaaa]

strings are objects-> compare objects (content) with the equals method and not with ==!
if("a".equals("a")).....
Java: ==, .equals(), compareTo(), and compare()

[Logik22]

Thank you. I have modified my code.

Did I do the "not equals" code correctly in the first If statement?

The reason I ask is because when I put in a valid answer (C,c, F, f) It displays my "Please input a valid answer. Valid answers are 'F', 'f', 'C', 'c'" message.

//Imports package to enable scanner to read user input
import java.util.Scanner;

//'TempConverter' Class
public class TempConverter
{

//'main' method
public static void main(String[] args)
{
//Calls the 'convert' class so the program can gather input, perform calculations, and output data.
convert();

//Calls 'exit' class to prompt user to exit or restart.
exit();

}



public static void convert()
{

//Creates variable for user input. User input should be 'C' or 'F'.
String TempScale;
//Creates variable for user inputted temperature. This is the number that will be converted.
String RawTemp;
//Variable to hold RawTemp conversion from String to Double so the calculation may be performed
Double Temp;
//Variable for converted temperature to be output to screen
Double CTemp;

//Output to prompt user for input
System.out.println("Please input 'C' to convert 'Fahrenheit to Celsius' or input 'F' to convert 'Celsius to Fahrenheit'.");

//Scanner to read user input
Scanner ScaleInput = new Scanner(System.in);

//Assigns 'TempScale' to user input
TempScale = ScaleInput.nextLine();

//Verifies user input valid answer
if(TempScale != "F" || TempScale != "f" || TempScale != "C" || TempScale != "c"){
	System.out.println("Please input a valid answer. Valid answers are F, f, C,  c");
	convert();
	
//Runs conversion
} else {
	
if(TempScale == "F" || TempScale == "f"){
	
//Confirms user input
System.out.println("You have select to convert from Celsius to Fahrenheit.");
//Asks user for temperature
System.out.println("Please input the Celsious temperature you want converted.");
//Reads input
Scanner TempInput = new Scanner(System.in);
//Assigns input to 'RawTemp'
RawTemp = TempInput.nextLine();
//Converts String 'RawTemp' to Double 'Temp'
Temp = Double.parseDouble(RawTemp);
//Converts to Fahrenheit
CTemp = (Temp*1.8) + 32;
//Outputs temperature in both measurements
System.out.println("Celcius: " + Temp);
System.out.println("Fahrenheit: " + CTemp);

} else {
	
	//Confirms user input
	System.out.println("You have select to convert from Fahrenheit to Celsius.");
	
	//Asks user for temperature
	System.out.println("Please input the Fahrenheit temperature you want converted.");
	
	//Reads input
	Scanner TempInput = new Scanner(System.in);
	
	//Assigns input to 'RawTemp'
	RawTemp = TempInput.nextLine();
	
	//Converts String 'RawTemp' to Double 'Temp'
	Temp = Double.parseDouble(RawTemp);
	
	//Converts to Fahrenheit
	CTemp = (Temp-32)/1.8;
	
	//Outputs temperature in both measurements
	System.out.println("Fahrenheit: " + Temp);
	System.out.println("Celsius: " + CTemp);	
}

}
}

public static void exit()
{
//Variable prompting user to exit
String ExitReply;
	
System.out.println("If you would like to exit the program please type 'exit', otherwise type 'retry' to restart the program.");

//Scanner to read user input
Scanner ExitInput = new Scanner(System.in);

//Assigns 'ExitReply' to user input
ExitReply = ExitInput.nextLine();

//Test output
System.out.println(ExitReply + " ECHO");

//Verifies user put in valid answer
if(ExitReply == "exit" || ExitReply == "Exit" || ExitReply == "Retry" || ExitReply == "retry"){
	
	//If-else statement to Retry or Exit program
		if(ExitReply == "Retry" || ExitReply == "retry"){
			//Test output
			System.out.println("test");
			//Restarts program
			convert();
			exit();
	} else {
		
		//Test output
		System.out.println("test2");
		
		//Closes program
		System.exit(0);
	} 

}
else{
	//Prompts user to put in valid response
	System.out.println("Please input either 'exit' or 'retry'.");
	exit();
}
}


}

[JosAH]

You're still trying to compare two Strings for (in)equality by using the == or != operator; don't do that, use the equals( ... ) method instead and read the API documentation for the String class.

kind regards,

Jos

[Logik22]

You're still trying to compare two Strings for (in)equality by using the == or != operator; don't do that, use the equals( ... ) method instead and read the API documentation for the String class.

kind regards,

Jos

Sorry, I thought I pasted the updated code but I must have still had the old code copied.

This is what i meant to post.

//Imports package to enable scanner to read user input
import java.util.Scanner;

//'TempConverter' Class
public class TempConverter
{

//'main' method
public static void main(String[] args)
{
//Calls the 'convert' class so the program can gather input, perform calculations, and output data.
convert();

//Calls 'exit' class to prompt user to exit or restart.
exit();

}



public static void convert()
{

//Creates variable for user input. User input should be 'C' or 'F'.
String TempScale;
//Creates variable for user inputted temperature. This is the number that will be converted.
String RawTemp;
//Variable to hold RawTemp conversion from String to Double so the calculation may be performed
Double Temp;
//Variable for converted temperature to be output to screen
Double CTemp;

//Output to prompt user for input
System.out.println("Please input 'C' to convert 'Fahrenheit to Celsius' or input 'F' to convert 'Celsius to Fahrenheit'.");

//Scanner to read user input
Scanner ScaleInput = new Scanner(System.in);

//Assigns 'TempScale' to user input
TempScale = ScaleInput.nextLine();

//Verifies user input valid answer
if(!TempScale.equals("F") || !TempScale.equals("f")|| !TempScale.equals("C") || !TempScale.equals("c")){
	System.out.println("Please input a valid answer. Valid answers are 'F', 'f', 'C',  'c'");
	convert();
	
//Runs conversion
} else {
	
if(TempScale.equals("F") || TempScale.equals("f")){
	
//Confirms user input
System.out.println("You have select to convert from Celsius to Fahrenheit.");

//Asks user for temperature
System.out.println("Please input the Celsious temperature you want converted.");

//Reads input
Scanner TempInput = new Scanner(System.in);

//Assigns input to 'RawTemp'
RawTemp = TempInput.nextLine();

//Converts String 'RawTemp' to Double 'Temp'
Temp = Double.parseDouble(RawTemp);

//Converts to Fahrenheit
CTemp = (Temp*1.8) + 32;

//Outputs temperature in both measurements
System.out.println("Celcius: " + Temp);
System.out.println("Fahrenheit: " + CTemp);

} else {
	
	//Confirms user input
	System.out.println("You have select to convert from Fahrenheit to Celsius.");
	
	//Asks user for temperature
	System.out.println("Please input the Fahrenheit temperature you want converted.");
	
	//Reads input
	Scanner TempInput = new Scanner(System.in);
	
	//Assigns input to 'RawTemp'
	RawTemp = TempInput.nextLine();
	
	//Converts String 'RawTemp' to Double 'Temp'
	Temp = Double.parseDouble(RawTemp);
	
	//Converts to Fahrenheit
	CTemp = (Temp-32)/1.8;
	
	//Outputs temperature in both measurements
	System.out.println("Fahrenheit: " + Temp);
	System.out.println("Celsius: " + CTemp);	
}

}
}

public static void exit()
{
//Variable prompting user to exit
String ExitReply;
	
System.out.println("If you would like to exit the program please type 'exit', otherwise type 'retry' to restart the program.");

//Scanner to read user input
Scanner ExitInput = new Scanner(System.in);

//Assigns 'ExitReply' to user input
ExitReply = ExitInput.nextLine();

//Verifies user put in valid answer
if(ExitReply.equals("exit") || ExitReply.equals("Exit") || ExitReply.equals("Retry")|| ExitReply.equals("retry")){
	
	//If-else statement to Retry or Exit program
		if(ExitReply.equals("Retry") || ExitReply.equals("retry")){
			//Restarts program
			convert();
			exit();
	} else {
		
		//Test output
		System.out.println("test2");
		
		//Closes program
		System.exit(0);
	} 

}
else{
	//Prompts user to put in valid response
	System.out.println("Please input either 'exit' or 'retry'.");
	exit();
}
}


}

[Fubarable]

Use a Venn diagram to check the logic of this:

if(!TempScale.equals("F") || !TempScale.equals("f")|| 
    !TempScale.equals("C") || !TempScale.equals("c")){

You'll then see why this is always true and how to fix it.

Also, please reduce your number of comments to a reasonable amount. All your copious comments do is to clutter your code making it near unreadable.

[Fubarable]

For example if A and B are mutually exclusive, (in your example, you can't have a String equal to both "F" and "f" at the same time... )

[Logik22]

Thanks for the help guys. I got that part working by changing it to:

if(!TempScale.equals("F") && !TempScale.equals("f") && !TempScale.equals("C") && !TempScale.equals("c")){
	System.out.println("Please input a valid answer. Valid answers are 'F', 'f', 'C',  'c'");
	convert();

But I don't understand why it works. I thought with this way it's saying "If Tempscale is equal to ALL 4 answers (F,f,C,c) then execute this code"


Where as with my original code

if(!TempScale.equals("F") || !TempScale.equals("f") || !TempScale.equals("C") || !TempScale.equals("c")){
	System.out.println("Please input a valid answer. Valid answers are 'F', 'f', 'C',  'c'");
	convert();

I thought it's saying "If TempScale is equal to anyone of the 4 answers (F, f, C, c) then execute this code".



As for the comments, I know I went a bit overboard on this and a lot of it could be trimmed down but in this situation it is necessary. Sorry if it made it any harder to help me.

[Fubarable]

The key is that you're using the not operator "!". Again read up on what Venn diagrams mean and then look at my pictures -- the answer is there in simple graphical form.

Or think of it like this:

if (foo != 1 || foo != 2) {
   // ... do something
}

Can you think of any situation where this is not true?

• If foo == 1, then it doesn't equal 2 and the statement is true.
• If foo == 2, then it doesn't equal 1 and the statement is true.
• If foo == something else, then it doesn't equal 1 and it doesn't equal 2 and the statement is true.
• Thus the statement is always true

Likewise for your code, the simple logic shown above applies:

if(!TempScale.equals("F") || !TempScale.equals("f") || !TempScale.equals("C") || !TempScale.equals("c")){
    System.out.println("Please input a valid answer. Valid answers are 'F', 'f', 'C',  'c'");
    convert();

• if TempScale equals "F", then it doesn't equal "f", "C", or "c", and the statement is true.
• if TempScale equals "f", then it doesn't equal "F", "C", or "c", and the statement is true.
• if TempScale equals "C", then it doesn't equal "F", "f", or "c", and the statement is true.
• if TempScale equals "c", then it doesn't equal "F", "f", or "C", and the statement is true.
• if TempScale equals anything else, then it doesn't equal "F", "f", "C", or "c", and the statement is true.
• Thus the statement is always true.

Make sense?

[Logik22]

Ahhhh I see. Makes sense now. Thanks!

[Fubarable]

You're welcome -- glad that you understand!

[Logik22]

You're welcome -- glad that you understand!

Thanks again for your help.



I will post the updated code in case anyone uses this thread as a reference later on.

//Imports package to enable scanner to read user input
import java.util.Scanner;

//'TempConverter' Class
public class TempConverter
{

//'main' method
public static void main(String[] args)
{
//Calls the 'convert' class so the program can gather input, perform calculations, and output data.
convert();

//Calls 'exit' class to prompt user to exit or restart.
exit();

}



public static void convert()
{

//Creates variable for user input. User input should be 'C' or 'F'.
String TempScale;
//Creates variable for user inputted temperature. This is the number that will be converted.
String RawTemp;
//Variable to hold RawTemp conversion from String to Double so the calculation may be performed
Double Temp;
//Variable for converted temperature to be output to screen
Double CTemp;

//Output to prompt user for input
System.out.println("Please input 'C' to convert 'Fahrenheit to Celsius' or input 'F' to convert 'Celsius to Fahrenheit'.");

//Scanner to read user input
Scanner ScaleInput = new Scanner(System.in);

//Assigns 'TempScale' to user input
TempScale = ScaleInput.nextLine();

//Verifies user input valid answer
if(!TempScale.equals("F") && !TempScale.equals("f") && !TempScale.equals("C") && !TempScale.equals("c")){
	System.out.println("Please input a valid answer. Valid answers are 'F', 'f', 'C',  'c'");
	convert();
	
//Runs conversion
} else {
	
if(TempScale.equals("F") || TempScale.equals("f")){
	
//Confirms user input
System.out.println("You have select to convert from Celsius to Fahrenheit.");

//Asks user for temperature
System.out.println("Please input the Celsious temperature you want converted.");

//Reads input
Scanner TempInput = new Scanner(System.in);

//Assigns input to 'RawTemp'
RawTemp = TempInput.nextLine();

//Converts String 'RawTemp' to Double 'Temp'
Temp = Double.parseDouble(RawTemp);

//Converts to Fahrenheit
CTemp = (Temp*1.8) + 32;

//Outputs temperature in both measurements
System.out.println("Celcius: " + Temp);
System.out.println("Fahrenheit: " + CTemp);

} else {
	
	//Confirms user input
	System.out.println("You have select to convert from Fahrenheit to Celsius.");
	
	//Asks user for temperature
	System.out.println("Please input the Fahrenheit temperature you want converted.");
	
	//Reads input
	Scanner TempInput = new Scanner(System.in);
	
	//Assigns input to 'RawTemp'
	RawTemp = TempInput.nextLine();
	
	//Converts String 'RawTemp' to Double 'Temp'
	Temp = Double.parseDouble(RawTemp);
	
	//Converts to Fahrenheit
	CTemp = (Temp-32)/1.8;
	
	//Outputs temperature in both measurements
	System.out.println("Fahrenheit: " + Temp);
	System.out.println("Celsius: " + CTemp);	
}

}
}

public static void exit()
{
//Variable prompting user to exit
String ExitReply;
	
System.out.println("If you would like to exit the program please type 'exit', otherwise type 'retry' to restart the program.");

//Scanner to read user input
Scanner ExitInput = new Scanner(System.in);

//Assigns 'ExitReply' to user input
ExitReply = ExitInput.nextLine();

//Verifies user put in valid answer
if(ExitReply.equals("exit") || ExitReply.equals("Exit") || ExitReply.equals("Retry") || ExitReply.equals("retry")){
	
	//If-else statement to Retry or Exit program
		if(ExitReply.equals("Retry") || ExitReply.equals("retry")){
			//Restarts program
			convert();
			exit();
	} else {
		
		//Confirms exit
		System.out.println("--END--");
		//Closes program
		System.exit(0);
	
	} 

}
else{
	//Prompts user to put in valid response
	System.out.println("Please input either 'exit' or 'retry'.");
	exit();
}
}


}

[Fubarable]

Note that your program uses recursion to solve it's problem: i.e., the method calls itself here:

 //Verifies user input valid answer
if(!TempScale.equals("F") && !TempScale.equals("f") && !TempScale.equals("C") && !TempScale.equals("c")){
    System.out.println("Please input a valid answer. Valid answers are 'F', 'f', 'C',  'c'");
    convert();   // ***** here the convert method calls itself *****

Unless I were specifically told my instructor to solve it this way, I wouldn't do this as it can lead to some traps. Instead I'd use a while loop and simply set the boolean variable used to exit the while loop from inside of this if condition or its else block:

boolean done = false;
while (!done) {
   if (!TempScale.equals... etc...) {
       // warn user that the wrong String was entered
   } else {
       done = true;
       // do other stuff that needs to be done in this else block...
   }

}