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I'm doing a small project in Java whilst I'm learning the language.
Basically what I'd like is for a user to input a string via JOptionPane.showInputDialog();, if that string is empty, I want it to make them re-enter a valid string and then the program will continue.
What I did consider doing is using goto but I read up on it and it said it's not good practice.
Any help would be greatly appreciated.
Thanks :)
I would do it in an infinite loop asking for input (using OptionPane.showInputDialog()).
Here you have some pseudo code:
message = ""
while message.equals(""):
message = ask_for_input() // (.trim() if needed)
end
You could do it in a loop. So you take a while-loop where the condition is that the input is empty. Then the message will pop up until the user entered something.
Despite goto is a reserved keyword in Java, it's actually (implicitly) meant for not being used.
JOptionPane.showInputDialog(...) returns a String.
I suggest using an infinite while loop and comparing it to empty, through String.isEmpty().
For instance:
String input = null;
while (true) {
input = JOptionPane.showInputDialog("Your input (not empty):");
if (!input.trim().isEmpty()) {
// TODO something with the input variable
break;
}
}
This is what do ... while loops are for. You could also use the Apache commons StringUtils class.
String input;
do {
input = JOptionPane.showInputDialog("Please enter your string");
} while (StringUtils.isBlank(input));
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I am in my first semester of a Java Course. I am struggling to understand how I put exclusiveness on a statement. I am writing a Class for an Object Couch. I have tried to build a well formed class, but for the outcome from my main, in the console it must only have 4 or 8 legs on the couch. There is no user input as I am hard coding the variables, but I want to be sure that if I hard code for 5 legs it will stop me or an error message will pop up. Any suggestions?
public void setNbrLegs(int nbrLegs){
if ((nbrLegs == 2) || (nbrLegs == 4)){
this.nbrLegs = nbrLegs;
}
}
I tried putting an "else" with a message that that number is bad, but what is did was bypass my error message and just insert the incorrect number ofLegs as 5.
Consider looking for the opposite: a condition where you must fail. From there, you can use runtime exceptions to ensure a few things:
The invalid state is not applied
A developer passing this invalid state will get an exception, and have a clear reason to fix their code
You no longer have to worry about invalid state further on in the method (i.e. legs will only be 2 or 4 further on).
In doing so, your method may end up looking like this:
public void setNbrLegs(int legs) {
if (legs != 4 && legs != 2) {
throw new IllegalArgumentException("Can only have 2 or 4 legs");
}
this.nbrLegs = legs;
}
This preconditional checking is also good to do early in your methods (fast-fail), as it will prevent excess work being done for a method that will only "fail".
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Here is my code, I am supposed to read in data such as AAABBBCCCDDD and output a3b3c3d3.
I have updated the code, and now the code compiles and runs, however nothing is output. I dont know if its the way im reading data in or if the code is incorrect.
String text;
FileReader data = new FileReader("input.txt");
BufferedReader in = new BufferedReader(data);
text=in.readLine();
in.close();
//Counter looks at length of data
int counter=0;
//Counter2 looks at current letter or number to make see if its the same then iterates it
int counter2=0;
while (text.charAt(counter)<=text.length())
{
while (text.charAt(counter)==text.charAt(counter2+1))
{
counter2++;
}
System.out.println(text.charAt(counter) + counter2);
counter=counter2;
}
The reason the compiler is complaining is because in this loop:
while (in.readLine()!=null)
{
text = in.readLine();
}
it's possible that the body of the loop will never get executed, which means it's possible that text will never be set to anything. And the Java compiler doesn't like it when you use a variable that may not have been set to anything.
But the whole loop is wrong anyway. You're only using one input string, so why is this a loop? Before we can help fix this problem, we need to know what you're trying to accomplish. And if you really do want a loop, it would be wrong to call in.readLine() twice as you have above, since that means it will read two lines each time through the loop.
Assuming you've properly imported all the java.io classes, here are the two problems causing compilation to fail:
String text;
This must be initialized to something. Such as
String text = null;
Possibly setting it in the while loop is not good enough.
The other problem is this variable, output doesn't exist anywhere, which is why this line won't compile:
System.out.println(output);
I think you mean for it to be text
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I am doing an assignment and I have to do several simple string manipulations. I think I have the last one figured out, and it works by itself, but it does not work when I put it together with the other string manipulations, giving me an arrayoutofbounds exception error. Any advice?
Here is the small code I made
public static void main (Strings[] args) {
Scanner sc = new Scanner(System.in);
String theSentence = sc.nextLine();
String [] theWords = theSentence.split(" ");
Arrays.sort(theWords);
System.out.println(theWords[1]);
System.out.println(Arrays.toString(theWords));
}
This does not work when it is put together with the rest of the code even though it works by itself. For reference, this code is supposed to take in a small sentence and give me the smallest word lexicographically. Ex: input: "4 WHAT WAIT IS THIS" output would be "IS"
The code is assuming that theWords will always have at least two elements in it. If the sentence provided by the user does not have any spaces, theWords will never get an element in position 1 and so the program will crash on System.out.println(theWords[1]);
In Java arrays are indexed from zero, where the 0th element is the first.
As Mark said you are assuming that there are always two words entered in this case. You should check the length of theWords before trying to access an element.
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So, I need to take the input I get from (for example)
JOptionPane.showInputDialog(null, "text");
(and if the user enters some text, say, "hello" it would be used as a message in
JOptionPane.showMessageDialog(null, "Hello");
I think I have to use a variable like:
variable=JOptionPane.showInputDialog(null, "text");
but how do I connect the two and what type will the variable have?
You can add it in one line,
JOptionPane.showMessageDialog(null,JOptionPane.showInputDialog(null,"Please enter a message"));
Or, you can create a string to hold a message:
String message = JOptionPane.showInputDialog(null,"Enter a message");
JOptionPane.showMessageDialog(null,message);
Note that first parameter may be null, in which case a default Frame is used as the parent, and the dialog will be centered on the screen (depending on the L&F).
Read about JOptionPane
Read the Oracle docs on variables. Then consult the javadoc for JOptionPane
String message = JOptionPane.showInputDialog(null, "text");
JOptionPane.showMessageDialog(null, message);
JOptionPane.showInputDialog("Provide Input"); This statement returns String value which can be use to pass in showMessageDialog. Refer below code
String ans=JOptionPane.showInputDialog("Give some input");
JOptionPane.showMessageDialog(null, ans);
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I have this xml file from where I'm reading this string,
http://localhost:8080/sdpapi/request/10/notes/611/
My question is how can I get just the 611, which is of variable, can be 100000, for example, from this string?
Split the string
String input = "http://localhost:8080/sdpapi/request/10/notes/611/";
String output = input.split("notes/")[1].split("/")[0];
output is the value you need
What language?
Anyway, in most cases it's a syntax like:
String.substring(begin, length);
... where 'begin' is the number of the letter in the string-1. For extracting http from the above string you would write
substring(0, 4);
In case you always need the last string between the last two '/'s, you can retrieve the position of the slashes with index-functions (as stated in the answer of #Liran for example).
// EDIT: In Java the second parameter of substring is not length, but endIndex:
String s = "http://localhost:8080/sdpapi/request/10/notes/611/";
s.substring(46, s.lastIndexOf('/'));
It depends on programming language you use, but Regular Expressions should be the same in most of them:
/(\d+)\/$/
well, it depend in what language are you writing... in c# for example
string s = #"http://localhost:8080/sdpapi/request/10/notes/611/";
s.SubString(s.LastIndexOf('/'));
or
Path.GetFileName(s);
for java
new File(s).getName();