I'm trying to do a "do while" loop with a nested if statement. I'm trying to compare two possible values for a String variable "word". If !word.equals "deeppan or thin" do something, else do something. But its not liking me using the or || comparator .. Any suggestions would be welcome.
do {
word = scan.next();
if ( !word.equalsIgnoreCase( "Deeppan" || "thin" ) ) {
System.out.print("Sorry you must specify a Deeppan or thin base, try again: ");
} else {
break;
}
} while ( true );
equalsIgnoreCase takes a single string argument, not a logical expression. You can combine them with || or && though:
if (!word.equalsIgnoreCase( "Deeppan") && !word.equalsIgnoreCase("thin" ))
You have to do it like this:
if (!word.equalsIgnoreCase("Deeppan") && !word.equalsIgnoreCase("thin")) {
Think about the || which i switched to &&, because the if should only be true, if the value is not the first AND not the second one!
This part is wrong, that's not how you use the boolean || operator, and anyway the logic is incorrect:
if (!word.equalsIgnoreCase("Deeppan" || "thin"))
It should be like this, comparison-operator-comparison, and notice the correct way to state the comparison for the effect you want to achieve:
if (!(word.equalsIgnoreCase("Deeppan") || word.equalsIgnoreCase("thin")))
Or equivalently, using De Morgan's laws (and easier to read and understand, IMHO):
if (!word.equalsIgnoreCase("Deeppan") && !word.equalsIgnoreCase("thin"))
You have a few issues going on. First:
"Deeppan" || "thin"
is attempting to use the boolean "OR" operator to compare two strings. The "OR" operator can only compare boolean results and returns a boolean that is the result of the comparison:
System.currentTimeMillis() == 123455667 || object.equals(this) // both sides are boolean results.
true || false // returns 'false'
But let's pretend for a second that "Deeppan" || "thin" is OK (remember, it isn't) and the compiler knows that you want to compare the two strings. It still leaves the issue that the OR operator returns a boolean result (true or false), which you are then attempting to pass into the method equalsIgnoreCase on the word variable. equalsIgnoreCase takes a String argument, not a boolean. This is the second compilation issue. As has been pointed out, what you need is to check for the conditions separately and OR the result to get the final boolean
if("Deeppan".equalsIgnoreCase(word) || "thin".equalsIgnoreCase(word)) {
// do something
}
("Deeppan" || "thin")
is a boolean expression. equalisIgnoreCase takes a string. Therefore you need to make two seperate calls and OR the (boolean) results
Related
I'm a beginner in coding. I was recently working with to create a chatting programme where a user will chat with my computer. Here is a part of the code:
System.out.println("Hello, what's our name? My name is " + answer4);
String a = scanner1.nextLine();
System.out.println("Ok, Hello, " + a + ", how was your day, good or bad?");
String b = scanner2.nextLine();
**if (b.equals("good"))** { //1
System.out.println("Thank goodness");
} else **if (b.equals("it was good"))** { //2
System.out.println("Thank goodness");
} else **if (b.equals("bad"))** { //3
System.out.println("Why was it bad?");
String c = scanner3.nextLine();
System.out.println("Don't worry, everything will be ok, ok?");
String d= scanner10.nextLine();
} else **if (b.equals("it was bad"))**{ //4
System.out.println("Why was it bad?");
String c = scanner3.nextLine();
System.out.println("Don't worry, everything will be ok, ok?");
String d= scanner10.nextLine();
}
if(age<18){System.out.println("How was school?");}
else if (age>=18){System.out.println("How was work?");}
The conditions of the if statements are in Bold (surrounded with **). In case of first and the second condition I want my application to do same thing. Similarly third and fourth condition. I thought it was possible to somehow group them in if statement.
I tried with below code but it doesn't compile:
if (b.equals("good"), b.equals("it was good")) {
System.out.println("Thank goodness");
} else if (b.equals("bad"),(b.equals("it was bad"))) {
System.out.println("Why was it bad?");
String c = scanner3.nextLine();
System.out.println("Don't worry, everything will be ok, ok?");
String d= scanner10.nextLine();
}
Can someone correct it for me?
You can use logical operators to combine your boolean expressions.
&& is a logical and (both conditions need to be true)
|| is a logical or (at least one condition needs to be true)
^ is a xor (exactly one condition needs to be true)
(== compares objects by identity)
For example:
if (firstCondition && (secondCondition || thirdCondition)) {
...
}
There are also bitwise operators:
& is a bitwise and
| is a bitwise or
^ is a xor
They are mainly used when operating with bits and bytes. However there is another difference, let's take again a look at this expression:
firstCondition && (secondCondition || thirdCondition)
If you use the logical operators and firstCondition evaluates to false then Java will not compute the second or third condition as the result of the whole logical expression is already known to be false. However if you use the bitwise operators then Java will not stop and continue computing everything:
firstCondition & (secondCondition | thirdCondition)
Here are some common symbols used in everyday language and their programming analogues:
"," usually refers to "and" in everyday language. Thus, this would translate to the AND operator, &&, in Java.
"/" usually refers to "or" in everyday language. Thus, this would translate to the OR operator, ||, in Java.
"XOR" is simply "x || y but both cannot be true at the same time". This translates to x ^ y in Java.
In your code, you probably meant to use "or" (you just used the incorrect "incorrect solution" :p), so you should use "||" in the second code block for it to become identical to the first code block.
Hope this helped :)
You're looking for the "OR" operator - which is normally represented by a double pipe: ||
if (b.equals("good") || b.equals("it was good")) {
System.out.println("Thank goodness");
} else if (b.equals("bad") || b.equals("it was bad")) {
System.out.println("Why was it bad?");
String c = scanner3.nextLine();
System.out.println("Don't worry, everything will be ok, ok?");
String d= scanner10.nextLine();
}
This is probably more answer than you need at this point. But, as several others already point out, you need the OR operator "||". There are a couple of points that nobody else has mentioned:
1) If (b.equals("good") || b.equals("it was good")) <-- If "b" is null here, you'll get a null pointer exception (NPE). If you are genuinely looking at hard-coded values, like you are here, then you can reverse the comparison. E.g.
if ("good".equals(b) || "it was good".equals(b))
The advantage of doing it this way is that the logic is precisely the same, but you'll never get an NPE, and the logic will work just how you expect.
2) Java uses "short-circuit" testing. Which in lay-terms means that Java stops testing conditions once it's sure of the result, even if all the conditions have not yet been tested. E.g.:
if((b != null) && (b.equals("good") || b.equals("it was good")))
You will not get an NPE in the code above because of short-circuit nature. If "b" is null, Java can be assured that no matter what the results of the next conditions, the answer will always be false. So it doesn't bother performing those tests.
Again, that's probably more information than you're prepared to deal with at this stage, but at some point in the near future the NPE of your test will bite you. :)
You can have two conditions if you use the double bars(||). They mean "Or". That means only ONE of your conditions has to be true for the loop to execute.
Something like this:
if(condition || otherCondition || anotherCondition) {
//code here
If you want all of conditions to be true use &&. This means that ALL conditions must be true in order for the loop to execute. if any one of them is false the loop will not execute.
Something like this:
if(condition && otherCondition && anotherCondition) {
//code here
You can also group conditions, if you want certain pairs of them to be true. something like:
if(condition || (otherCondition && anotherCondition)) {
//code here
There is a simpler way.
if (b.contains("good")) {
...
}
else if (b.contains("bad")) {
...
}
I want to be able to print a string that doesn't contain the words "Java", "Code" or "String", though I am unsure on how to achieve this as I thought this would be achieved by using '!' (NOT). However, this is not the case as the string is still printed despite the inclusion of the words I want to forbid.
Any advice on how to achieve this would be greatly appreciated, thanks in advance.
System.out.println("Type in an input, plez?");
String userInput6 = inputScanner.nextLine();
if (!userInput6.toLowerCase().contains("Java") || !userInput6.toLowerCase().contains("Code") || !userInput6.toLowerCase().contains("String")) {
System.out.println("I see your does not string contain 'Java', 'Code' or 'String, here is your string:- " + userInput6);
} else {
System.out.println("Your string contains 'Java, 'Code' or 'String'.");
}
I thought this would be achieved by using '!' (NOT)
It is. You just haven't applied it correctly to your situation:
You start with this statement:
userInput6.toLowerCase().contains("java") ||
userInput6.toLowerCase().contains("code") ||
userInput6.toLowerCase().contains("string")
which checks if the input contains any of these, and you wish to negate this statement.
You can either wrap the entire statement in parentheses (()) and negate that:
!(userInput6.toLowerCase().contains("java") ||
userInput6.toLowerCase().contains("code") ||
userInput6.toLowerCase().contains("string"))
or apply the DeMorgan's law for the negation of disjunctions which states that the negation of a || b is !a && !b.
So, as Carcigenicate stated in the comments, you would need
!userInput6.toLowerCase().contains("java") &&
!userInput6.toLowerCase().contains("code") &&
!userInput6.toLowerCase().contains("string")
instead.
Your statement is simply checking if the string doesn't contain at least one of these substrings. This means the check would only fail if the string contained all of these strings. With ||, if any operand is true, the entire statement is true.
Additionally, mkobit makes the point that your strings you are checking for should be entirely lowercase. Otherwise, you are checking if a .toLowerCased string contains an uppercase character - which is always false.
An easier way to think of it may be to invert your if statement:
if (userInput6.toLowerCase().contains("Java") ||
userInput6.toLowerCase().contains("Code") ||
userInput6.toLowerCase().contains("String")) {
System.out.println("Your string contains 'Java, 'Code' or 'String'.");
} else {
System.out.println("I see your does not string contain 'Java', 'Code' or 'String, here is your string:- " + userInput6);
}
Since you're using logical OR, as soon as one your contains checks it true, the entire condition is true. You want all the checks to be true, so you need to use logical AND (&&) instead
As #mk points out, you have another problem. Look at:
userInput6.toLowerCase().contains("Java")
You lower case the string, then check it against a string that contains an uppercase. You just removed all uppercase though, so that check will always fail.
Also, you can use regexp :)
boolean notContains(String in) {
return !Pattern.compile(".*((java)|(code)|(string)).*")
.matcher(in.toLowerCase())
.matches();
}
Or just inline it:
System.out.println("Type in an input, plez?");
String userInput6 = inputScanner.nextLine();
if (!Pattern.compile(".*((java)|(code)|(string)).*")
.matcher(userInput6.toLowerCase())
.matches()) {
System.out.println("I see your does not string contain 'Java', 'Code' or 'String, here is your string:- " + userInput6);
} else {
System.out.println("Your string contains 'Java, 'Code' or 'String'.");
}
I cannot for the life of me figure out why this code loops indefinitely when "turnOrder" is set to "first." It seems to be something about the "or" operator in the "do while loop." But I have no idea how to properly format it.
String turnOrder;
do {
Scanner to = new Scanner(System.in);
turnOrder = to.nextLine();
if ((!"first".equalsIgnoreCase(turnOrder)) || (!"second".equalsIgnoreCase(turnOrder))) {
System.out.println("Type your answer as 'first' or 'second.' Without the punctuation.");
} else {}
} while ((!"first".equalsIgnoreCase(turnOrder)) || (!"second".equalsIgnoreCase(turnOrder)));
It loops cause when you type "first", it returns false in
!"first".equalsIgnoreCase(turnOrder), BUT
it return true in
!"second".equalsIgnoreCase(turnOrder))
false OR true = true, so it will keep looping
You should always reduce your logic operations to their simplest form.
"((!"first".equalsIgnoreCase(turnOrder)) || (!"second".equalsIgnoreCase(turnOrder)))"
can be simplified using De Morgan's Laws to
!("first".equalsIgnoreCase(turnOrder) && "second".equalsIgnoreCase(turnOrder))
Of course turnOrder cannot be "first" and "second" simultaneously. It will always evaluate to true, thus your while loop will loop indefinitely.
while ((!"first".equalsIgnoreCase(turnOrder)) || (!"second".equalsIgnoreCase(turnOrder)))
This statement will always be true until you come up with a turnOrder value that equalsIgnoreCase-s to "first" and "second" simultaneously. Good luck with that! Perhaps you meant...
while (
!(
"first".equalsIgnoreCase(turnOrder) ||
"second".equalsIgnoreCase(turnOrder)
)
)
I'm quite new to Java, and can't figure out how to use 'or'. What is the Java equivalent?
I've already tried && and || but eclipse does not recognise it.
This is part of my code:
if (action.equals ("run") || ("sprint")) {
System.out.println("you ran");
}
else {
System.out.println("else");
}
I've already tried && and || but eclipse does not recognise it.
That's very strange, but just to cover the basics: Let's assume you have the variable a and it contains the value 5. Then:
if (a == 5 || a == 7)
...will be true, because the first part of the expression (a == 5) is true. So the statement "a equals 5 or a equals 7" is true.
The || operator can only be used, in Java, where a boolean (true or false) expression is expected, such as in an if statement like the above. So pretty much in an if or a conditional operator (that ?...: thing, sometimes called the ternary operator).
Re your edit, the problem is that both sides of your || operator aren't true or false ("boolean") expressions. Your statement:
if (action.equals ("run") || ("sprint")){
breaks down like this:
if (
action.equals ("run")
|| // ("or")
("sprint")
)
the second part of that isn't a true/false, it's a string. The correct way to express that in Java (or nearly any other programming language) is:
if (action.equals ("run") || action.equals ("sprint")){
Now both sides of the || result in true/false exprssions:
if (
action.equals ("run")
|| // ("or")
action.equals ("sprint")
)
The reason for this is that the second part may have nothing whatsoever to do with action, and so the compiler can't assume you mean to re-use it in the second part of the expression. You might, for instance, want to use || with two completely unrelated things:
if (action.equals("run") || somethingElse.equals("run")) {
Ok. ("sprint") is not a Boolean expression. Since a if condition expects a Boolean expression your code returns an error. You should change the line with:
if (action.equals ("run") || action.equals("sprint")){
The equals method returns a boolean and the || operator wants two booleans on each side.
You're doing an action.equals("run") on one side but then a ("sprint") on the other which isn't a boolean expression.
Change your code like so:
if (action.equals("run") || action.equals("sprint")){
This question already has answers here:
How do I compare strings in Java?
(23 answers)
Closed 8 years ago.
I'm trying to make a simplified version of Black Jack in Java using eclipse. I'm trying to make it so the player types 'hit' or 'stand', and while they haven't, it keeps prompting them to do so.
while (hitorstand != ("hit") || hitorstand != ("stand"))
{
System.out.println("Would you like to hit or stand?(1 for hit, 2 for stand)");
hitorstand = scan.nextLine();
hitorstand.toLowerCase();
}
if (hitorstand.equals("hit"))
{
playercard3 = random.nextInt(10) +2;
System.out.println(""+playercard3);
}
else if (hitorstand.equals("stand"))
{
System.out.println("You had a total value of " + playercardtotal + ".");
if (hiddendealercard == card2)
When I run it, no matter what I type it cannot escape the while loop. I know it would work if I used numbers but I really want to learn how to use words as input.
while (hitorstand != ("hit") || hitorstand != ("stand")) // This is not the right way
Use the equals() method for String value comparison. == is for object reference comparison.
while (!hitorstand.equals("hit") || !hitorstand.equals("stand")) // This is
I'm not sure why you'd use the != in the while loop condition, whereas you've properly used (hitorstand.equals("hit")) just below the while, in a if statement.
Also, there seems a minor mistake in the while loop block.
hitorstand.toLowerCase(); // This does nothing
As Strings are immutable in java, you need to assign back the changed string to be able to see the changes
hitorstand = hitorstand.toLowerCase(); // Assigning back the lowercase string back to hitorstand
You need to use .equals(..) instead of ==. This is because == is used for reference equality, while .equals() is simply for value equality.
For example:
while(!hitorstand.equals("hit") || !hitorstand.equals("stand"))
Comparing hitorstand != ("hit") you actually compare object references not the String value itself. To compare strings you need to use equals method. In java every class inherits equals ( from Object ) and it can be overriden for custom object comparison
Try this:
while (!hitorstand.equals("hit") || !hitorstand.equals("stand")){
Adding to the answers, a good rule of thumb is to use .equals() with strings and == with integer values or variables with integer values (or the value null).
One way you could do this would be to use a character. For example: instead of
while (hitorstand != ("hit") || hitorstand != ("stand"))
you could have it check for the first character in the string using the charAt() command with the index of the string in the parenthesis. So since your looking for the first character, it would be at index 0.
while (x != 'h' || x != 's')
x being a char.
Inside your while loop,
System.out.println("Would you like to hit or stand?");
hitorstand = scan.nextLine();
hitorstand.toLowerCase();
x = x.charAt(0); // you would just add this line. This gets the character at index 0 from the string and stores it into x. So if you were to type hit, x would be equal to 'h'.
Your if statement could stay the same or you could also change the condition to (x == 'h') and (x == 's'). That's up to you.