I already know how to compare floats and this is not the question.
When I compare float I cannot just do that:
if(flot1 == flot2) {
// do something
}
Indeed I was always taught to do something like this:
if(Math.abs(float1 - float2) < epsilon) {
// do something
}
But the question is when I use float wrappers... for example there is something as simple as the method equal():
if(floatWrapper1.equals(floatWrapper2)) {
// do something
}
But reading the documentation that this is equivalent to:
if(floatWrapper1.floatValue() == floatWrapper2.floatValue()) {
// do something
}
That is the same like the example (2) that is wrong for the purpose of comparison.
Looking in internet I then found some examples like this:
if(Float.compare(flotWrapper1, floatWrapper2) == 0) {
// do something
}
But, I was wonder if this is right neither. How should I then compare two float wrappers?
The simple answer is because of Auto boxing, comparing Floats is no different than comparing floats. Save for a null pointer check, you can treat them equivalently.
Related
I'm new to java and I was wondering if there was an easier way to write
if(a == 10 || b == 10){
//stuff
}
In my mind I tried something like this:
if(a||b == 10){
//stuff
}
because IMO that makes a lot of intuitive sense, but it's not a thing.
if you're only comparing a few values then you might as well proceed with the current approach as there is nothing in place to make it shorter. However, if you're repeating your self many times, then you can create a helper function to do the work for you.
i.e
static boolean anyMatch(int comparisonValue, int... elements){
return Arrays.stream(elements)
.anyMatch(e -> e == comparisonValue);
}
then call it like so:
if(anyMatch(10, a, b)){ ... }
That's not going to work like that. You're checking the value of two variables against a value, which ends up being two checks, if(a == 10 || b == 10).
However, you can modify this check to this code:
if(Arrays.asList(a,b).contains(10))
It results in the same behavior, but this is neither shorter nor easier to read.
Yeah turns out there isn't a way to make it shorter.
No, we can't do it because in case of java, there is no option for comparison of variables like that.
Even you couldn't write like this
if(a||b){ //staff }
but if you would write then you will get this error message
error: bad operand types for binary operator '||'
Not shorter, but more "intuitively" readable:
boolean condA = (a == 10);
boolean condB = (b == 10);
if(condA || condA){
//stuff
}
always keep in mind, the goal isn't to write shortest possible code, but best maintainable code.
I have a string that I would like to convert into an integer before storing it as a property of an object. Although I can use regular if statements, I wanted to use a ternary operation to build my understanding of it. Here is the code I've tried
field_num = (((boolean bool_is_int = is_integer(string)) == true) ? (Integer int = Integer.parseInt(string)) : null);
What I'm trying to do (very basically) is set "field_num" (which is of type int) to the value of "string" if it is equal to an integer (by first converting it). is_integer is a function I have to check if a string is equal to an integer. It returns a boolean value.
Thanks for any help.
I would do something like this:
Integer theint = is_integer(thestr) ? Integer.parseInt(thstr) : null;
You cannot assign NULL to an intrinsic int but you can to an Integer object. Typically, of course, you'd simply rely on the parseInt() call throwing an exception rather than explicitly testing for integerness of the string beforehand.
field_num = is_integer(string) ? Integer.parseInt(string): -1;
In plain english this says if 'string' is an integer then parse string for the int and set it to field_num otherwise, set it to -1. -1 is arbitrary. you should instead use a number that is invalid for field_num.
You do not need is_integer(string) == true because that evaluates to the same thing as is_integer(string). You also don't need to set the boolean bool_is_int because unless you actually want that value later in the program.
You should just use an if/else statement. The Ternary operator is useful when you you want to set a variable to one of two values based on a condition. In your example, you don't want to set the value if the string is not an integer so ternary doesn't fit the situation well.
Keep it simple :)
int field_num = isInt(string) ? Integer.parseInt(string) : Integer.MAX_VALUE;
if (field_num == Integer.MAX_VALUE) {
// error; string is not a valid representation of int
}
To determine Whether a String represents an int value :
public static boolean isInt(String s) {
try {
Integer.parseInt(s);
} catch(NumberFormatException e) {
return false;
}
return true;
}
[Corrected]
Learn one thing at a time.
First, the ?: operator (more often referred to as the conditional operator, or the if/else operator; "ternary" just means it takes three arguments, and it's the only C operator that does so, hence the confusion)...
field_num = is_integer(string) ? Integer.parseInt(string) : null;
Ahhh. So field_num is an Integer. Would have help if you'd said that.
Second: Assignment-in-passing. If you don't know that you need to do this, and you can't make it perfectly obvious what you're doing and why, DON'T. It's hard to read, and it's rarely appropriate.
Also, "int" is not a legal variable name.
But if you insist:
Integer myint;
boolean bool_is_int;
field_num = (bool_is_int = is_integer(string)) ? (myint = Integer.parseInt(string)) : null;
What's myint's value in the false/else case? It's left as whatever it had been set to previously. This might be what you intended, but it's very hard for someone reading your code to understand.
In most cases, unless the ?: is a very simple one that can be read at a glance -- (foo!=null) ? foo.doSomething() : defaultValue -- you're better off using a real if/then/else statement. It's likely to be just as efficient after the compiler and JIT are done with it, and it'll be a lot easier to maintain.
i was trying to write some C++ codes into java, now i have writter following code into java but it is throwing errors!
if(ShapeNotFound && xd*yd - nPixel[k] < xd+yd) // Condition for RECTANGLE
{
System.out.print("\n "+in+" \t Rectangle \n");
fileWriter3.write("\n "+in+" \t Rectangle \n");
Shape[k] = 2;
ShapeNotFound = 0;
}
I am getting following error :
The operator && is undefined for the argument type(s) int, boolean
Please help, tell me how to write the above if condition correctly in java
C and C++ both assume that for integers 0 is false and all other values are true.
Java does not make the same assumption so you need to add a check for int!=0 into the expression i.e.:
if((ShapeNotFound!=0) && (xd*yd - nPixel[k] < xd+yd))
Or alternatively your ShapeNotFound variable should be of type boolean not int.
It would be worth converting variable names etc to Java style guidelines as well.
Java can not convert int into boolean automatically.
It looks like ShapeNotFound is an integer, but you're implicitly treating it like a boolean (true or false). Java only likes genuinely boolean expressions, so you'll need to change the condition to something like this:
if (ShapeNotFound != 0 && xd*yd - nPixel[k] < xd+yd)
For readability, I'd suggest putting some brackets round each part of the condition. That's an issue of personal preference though.
This question already has answers here:
Why does my if condition not accept an integer in java?
(7 answers)
Closed 3 years ago.
I'm new at Java. I'm looking for some help with homework. I wont post the full code I was doing that originally but I dont think it will help me learn it.
I have a program working with classes. I have a class that will validate a selection and a class that has my setters and getters and a class that the professor coded with the IO for the program (it's an addres book)
I have a statement in my main like this that says
//create new scanner
Scanner ip = new Scanner(System.in);
System.out.println();
int menuNumber = Validator.getInt(ip, "Enter menu number: ", 1, 3);
if (menuNumber = 1)
{
//print address book
}
else if (menuNumber = 2)
{
// get input from user
}
else
{
Exit
}
If you look at my if statement if (menuNumber = 1) I get a red line that tells me I cannot convert an int to boolean. I thought the answer was if (menuNumber.equals(1)) but that also gave me a similar error.
I'm not 100% on what I can do to fix it so I wanted to ask for help. Do I need to convert my entry to a string? Right now my validator looks something like:
if (int < 1)
print "Error entry must be 1, 2 or 3)
else if (int > 3)
print "error entry must 1, 2, or 3)
else
print "invalid entry"
If I convert my main to a string instead of an int wont I have to change this all up as well?
Thanks again for helping me I haven't been diong that great and I want to get a good chunk of the assignment knocked out.
if (menuNumber = 1)
should be
if (menuNumber == 1)
The former assigns the value 1 to menuNumber, the latter tests if menuNumber is equal to 1.
The reason you get cannot convert an int to boolean is that Java expects a boolean in the if(...) construct - but menuNumber is an int. The expression menuNumber == 1 returns a boolean, which is what is needed.
It's a common mix-up in various languages. I think you can set the Java compiler to warn you of other likely cases of this error.
A trick used in some languages is to do the comparison the other way round: (1 == menuNumber) so that if you accidentally type = you will get a compiler error rather than a silent bug.
This is known as a Yoda Condition.
In Java, a similar trick can be used if you are comparing objects using the .equals() method (not ==), and one of them could be null:
if(myString.equals("abc"))
may produce a NullPointerException if myString is null. But:
if("abc".equals(myString))
will cope, and will just return false if myString is null.
I get a red line that tells me I cannot convert an int to boolean.
Thats because = is an assignment operator. What you need to use is == operator.
A single equal sign is assignment: you assign value to a variable this way. use two equal signs (==) for comparison:
if ($menuNumber = 1) {
Update: forgot dollar sign: $menuNumber
It seems logical that there should be some simple method to check which DatePicker object comes first but I can't find done.
// so if you had two objects
final DatePicker start_datepicker = (DatePicker)findViewById(R.id.DatePickerStart);
final DatePicker end_datepicker = (DatePicker)findViewById(R.id.DatePickerEnd);
// I was thinking something along the lines of:
if (end_datepicker > start_datepicker) {
// something
}
// or is there something like
if (end_datepicker.isLarger(start_datepicker)) {
// Something
}
Is this possible or does anyone know of something simple along these lines to compare to dates?
A DatePicker is a UI widget for displaying a date. You don't set it by assignment (as in your code) but by calling it's init method. Typically you would then track the date using an OnDateChangedListener. Nevertheless, you can compare the current dates displayed on two such widgets with something like this:
/** Returns a number <0, 0, or >0 when dp1 displays a date <, =, or > dp2. */
public int compare(DatePicker dp1, DatePicker dp2) {
int compare = dp1.getYear() - dp2.getYear();
if (compare == 0) {
compare = dp1.getMonth() - dp2.getMonth();
if (compare == 0) {
compare = dp1.getDay() - dp2.getDay();
}
}
return compare;
}
You should take the resulting values from the date pickers and convert them to Date objects which will then allow you to easily compare the values rather than going the route of writing your own Comparator that relies on the UI component.
I actually wrote a Java class specifically to handle this situation for Android. Feel free to use it and include it in your app! It's documented, as well.
Date has before() and after() methods.. just for that.