In C++ windows.h FALSE is defined as integer which makes sense for some special logic cases, but in Java java.lang.Boolean.FALSE is defined as boolean and assigned to false
public static final Boolean FALSE and I've seen some people use it.
My question: is there a performance difference between false and Boolean.FALSE? in general why do people go and Boolean.FALSE?
See http://docs.oracle.com/javase/7/docs/api/java/lang/Boolean.html.
Boolean.TRUE and Boolean.FALSE are not boolean, they are Boolean. They are static instances of the two Boolean wrapper objects that correspond to the boolean values true and false.
Boolean is similar to an enum. The TRUE and FALSE instances are the instances returned by Boolean.valueOf().
As for performance of primitive vs. wrapper; there is no difference that you would ever need to be concerned about. The TRUE and FALSE static instances help performance a bit, and the javadocs recommend using Boolean.valueOf() as opposed to new Boolean(...) for that reason. The true and false boolean values are a little "lower level", but if you are storing them in a Boolean (as opposed to boolean) anyways it's irrelevant.
You should use whichever makes the most sense for your code and leads to the best readability (and definitely don't start going down the path of thinking of microoptimizations like primitive vs. wrapper types). If you are using a Boolean, use the object values. If you are using a boolean, use the primitive values. If you are deciding between Boolean vs boolean, use whatever is more appropriate (e.g. a Boolean can be null, which may be useful, and also you can't use primitive types for generic type parameters; on the other hand, a boolean can never be null which could be equally useful).
Also note that auto boxing converts the primitive types to one of those two static Boolean instances, e.g.:
Boolean a = true;
assert(a == Boolean.TRUE);
As an aside, since you mentioned it: FALSE is defined in windows.h for two reasons: 1) Because windows.h has been in use since C-only days, and C does not have a native bool type, and 2) it is traditional Microsoft practice to define data types and values with known, explicit sizes and values, esp. for passing data to Windows API functions across DLL boundaries (beyond the scope of this question) and for integrating with other languages that have different representations of "true" and "false". It is entirely unrelated to the reasons for Boolean.FALSE in Java.
false is a primitive and Boolean.FALSE is an object, so they're not really comparable.
If you assign false to a Boolean variable, like this:
Boolean b = false;
Java's auto boxing occurs to convert the primitive into an object, so the false value is lost and you end up with Boolean.FALSE anyway.
In terms of performance, using a primitive variable would slightly out-perform using a wrapper Boolean object, but your choice should be based on readability and basic design decisions rather than on "performance".
Boolean comes in handy when you need a tri-state variable.
Also, you might want to check out this autoboxing and unboxing tutorial, as well as the rules for how it works.
It is a very strange question, because false is the value of primitive type boolean, while Boolean.FALSE is a variable of reference type Boolean. Its value is reference to the object of type Boolean which internal boolean state is false.
In regards to performance, Boolean.FALSE will return a Boolean object, which might give you more flexibility to work with.
The primitive alternative takes up less memory
First of all, if you are unclear with this, you need to know that in Java numericals cannot be implicitly cast to booleans, e.g. you cannot compile something like:
int a = 1;
if(a){
//something, something
}
Second, some considerations about performance.
There's always a tradeoff.
When using primitive type boolean, performance should be better because you're using a value directly, which is either true or false (obviously, byte-encoded).
When using object type Boolean, a variable/field will hold a value, but that value cannot be immediately used, as that value is in fact the reference to an object, so you might have a performance penalty. Of course, this penalty is not significant in most cases. And, if you develop a time-critical application, most likely you are not using Java :). Nevertheless, using object types might bring some benefits in development process and safety in use cases implementation (e.g. it allows nulls, which is critical when you map JPA entities to relational tables and there are bit-typed columns that allow nulls; and this is only one scenario where object type is better).
In the end, be aware of boxing/un-boxing, which allows developers to use boolean-typed variables almost everywhere a Boolean-typed variable is expected (and the other way around).
Boolean is wrapper class for boolean primitive type, same as we have Integer for int.
Boolean has many methods to play around primitive type boolean
http://docs.oracle.com/javase/6/docs/api/java/lang/Boolean.html
Boolean a = null;
if (a) {
// NullPointerException
}
if (a != false) {
// NullPointerException
}
// Caution, comparing by reference, meaning 2 Booleans with same value could be different
if (a != Boolean.FALSE) {
System.out.println("But this one works");
}
Related
I'm creating trie node class, which contains field with logical type and I don't know what will be better use boolean or Boolean.
I know that one instance of Boolean takes 16 Bytes and 4 bytes takes it reference in 32-bit VM. But Boolean have constants Boolean.TRUE and Boolean.FALSE, what can be used for space optimization. So application wiil takes 4*N+32 Bytes, where N is number of nodes, yes?
As far, as I know boolean value takes 4 bytes (in array it optimize to 1 byte per element) in 32-bit VM too)
However I can use code like this
boolean EOW = Boolean.TRUE;
but how many space it will take and how many time wiil take autboxing/inboxing?
So what will be better to use to optimize space usage and time?
And could you answer me how many space it tales on 64-bit VM?
Instead of this:
boolean EOW = Boolean.TRUE;
Just write this:
boolean EOW = true;
There is no reason to use Boolean.TRUE, it will be auto-unboxed to the primitive value true anyway, it's more efficient and less verbose to use the value true directly.
Only use wrapper classes such as Boolean when you have a good reason to do so - otherwise, use primitive types such as boolean. One reason to use a wrapper is when you need to store values in a collection (such as an ArrayList) - collection classes can only hold objects and not primitive values, so you'll have to use the wrapper class in that case.
Using Boolean objects is never more efficient than using boolean primitive values.
Note that primitive values are just values, not objects. If you use the value true ten times in your code, there will not be ten duplicate objects in memory.
Just use the primitive type boolean with true and false. Primitive types take less memory, work with better performance and are null-safe.
I expect the exact code, that you pasted, to be optimized to boolean EOW = true;, so it shouldn't be unboxed at all, but if there's no such an optimization, then you'll haven't any memory affected, because you use the static field, which will be initialized only once. Nevertheless, you still will lose one operation on imlicit running method booleanValue(), which will just return stored value. Actually, I don't have any idea, why you would want to have such an expression.
My bean is as below
private boolean myBoolean;
public boolean isMyBoolean() {
return myBoolean;
}
public void setMyBoolean(
boolean myBoolean) {
this.myBoolean = myBoolean;
}
Now when I use setter for the above Boolean field then what should be the efficient way to do it
setMyBoolean(true);
or
setMyBoolean(Boolean.TRUE);
I know that autoboxing will take care and both will work But I don't know what is the efficient way in this example. So my question is which of both should I use to write an efficient code OR both are equally good
TIA
Use the first one. More readable. You don't need to concern about the performance issue here, although the second one will involve auto-boxing and comparatively slower (again, you don't need to think about it).
Only consider code readability in this type of cases, and remember that primitives will always be faster than objects.
imho
setMyBoolean(true);
Primitives always do favor than Wrappers.Where ever I am able to use primitives,I go for them
Because while run time, If we use Wrappers Boxing conversions and Unboxing Conversions happens at Runtime,Obviously that takes more time.
In your case
At run time, boxing conversion proceeds as follows:
If p is a value of type boolean, then boxing conversion converts p into a reference r of class and type Boolean, such that r.booleanValue() == p
If you use primitive there,Obviously you save that time.
The reason
boolean boolVar = Boolean.TRUE;
works is because of autounboxing, a Java 5 feature that allows a wrapper object to be converted to its primitive equivalent automatically when needed
as you can understand, setting is faster then autounboxing and then setting...
It does not matter. At the very end when your code is compiled the bytecode generated will end up using the boolean data type on the JVM.
What I am trying to say is, on compile time, such a simple code like this will be optimized automatically for the JVM. It does not matter which way you use, remember that the compiler will end up translating this into bytecode and JVMs nowadays do this kind of optimizations all the time.
If you are skeptical on this, you can try both ways and use a profiler on your code. You will be amazed.
Boolean.TRUE is a wrapper object for boolean.
Boolean class implementation from Sun SDK:
public final class Boolean ...
{
private final boolean value;
public static final Boolean TRUE = new Boolean(true);
public static final Boolean FALSE = new Boolean(false);
...
}
when you use setMyBoolean(Boolean.TRUE);:
VM creates Boolean object (in heap) and the saves the value to true.
Unboxes the created object and finally assigns primitive true to myboolean.
when you use setMyBoolean(true);: only step 2 will be performed from above. Thus faster!
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So, according to wikipedia and others, a boolean values should have only 2 states: 0 or 1; true or false; yes or no; and so on...
OK, correct me if I'm wrong, but, Java Boolean wrapper let developers have 3 states: true, false and null.
Isn't that wrong?
I know that it could be explained with something like "Boolean is an object" etc etc, but, it would be really great if javac automagically "wrap" null to false, IMHO.
My point is: this behavior let developers do a lot of crap, because they use Boolean instead of a proper object type.
Anyway, what do you think about it? Am I following a wrong line of thinking.. or is it really "wrong"?
EDIT
I know what is null, the differences between boolean and Boolean, etc etc etc (I have 3-year+ exp with java).
My point is about the concept itself, like in Ruby, for example, if I do something like if something, if this something instance is nil, it will be false.
And I'm not saying that Java is crap or something like, I use it everyday.
null represents the absence of a value, whereas true and false are definite values. It's the difference between knowing something, either affirmatively or negatively, and not knowing it at all. That's one way to think of it.
Technically the reason a Boolean can be null is because it's an object reference, not a boolean value itself, a confusion that autoboxing might be causing for you. It used to be that you had to manually create Boolean objects to contain boolean values and manually extract the boolean values from Boolean objects. Since Java 5, the compiler will take care of this for you.
The value of the boolean contained by a Boolean object can either be true or false, but an object variable may not be pointing to an object at all, in which case the value of the reference is null.
Why is there a difference between boolean and Boolean you might ask? Well, in Java, unlike a lot of newer languages, the primitive types are not classes, and primitives are not objects. When you want to treat them as such, like when you want to pass by reference or call methods on them or put them in collections, you have to box them up in their respective primitive wrapper classes.
If the tri-valued nature of Boolean isn't right for you, don't use it. Use boolean. There are times when you need Boolean, when you are working with an Object-oriented interface. When that happens, you use Boolean.
boolean is a primitive type which represents the concept you are describing, a type with two possible values: true and false.
Boolean is different type. It's an Object which holds a boolean value. If the object doesn't exist, then the reference is null. It's not the boolean object which is null, it's the reference to a boolean object which is null.
Though their names are similar, don't conflate boolean and Boolean. They are distinct types for good reason.
Since you have a boolean which can be two states, it doesn't make sense to use Boolean unless
you need the three states
you are using an API which means you have to.
In general, always use a primitive if you can unless a) you need a null value b) you have to due to an API.
What you imply is that a wrapper should mimic the strict behavior of the primitive 'real' boolean. Thats the problem. A Boolean is not conceptually the same as a boolean (note capitalization).
The primitive boolean provides what is described in Wikipedia as a boolean.
The Boolean (java.lang.Boolean) is not called a wrapper just for show. It is conceptually an Object that contains a boolean. So references to a Boolean are references, nothing in common with a boolean. Thus the rules for references apply, not primitives.
Its quite simple and logical if you take this viewpoint.
You are confusing with primitive boolean and primitive wrapper Boolean. Indeed boolean can be true or false only.
Boolean instance can hold true or false too. But if instance does not exist the reference is null as any not initialized reference.
null means "I don't have an object here". The Boolean true object is a wrapper around the primitive boolean true, but it is still an object. Note that the following code throws a NullPointerException
public static void main(String[] args) {
Boolean myBool = null;
boolean primBool = myBool;
System.out.println(primBool);
}
Null makes it nullable , when you create a database for example it has a table with below columns :
Col-1 : Hour (nvarchar)
Col-2 : Minute (nvarchar)
Col-3 : IsDay (bool)
So if the hour is 18 and minute is 00 what is the value for IsDay ? (it is nor true or false) it is null at this time...
Reference: http://java.sun.com/j2se/1.5.0/docs/guide/language/autoboxing.html
"If your program tries to autounbox null, it will throw a NullPointerException."
javac will give you a compile-time error if you try to assign null to a boolean. makes sense. assigning null to a Boolean is a-ok though. also makes sense, i guess.
but let's think about the fact that you'll get a NPE when trying to autounbox null. what this means is that you can't safely perform boolean operations on Booleans without null-checking or exception handling. same goes for doing math operations on an Integer.
for a long time, i was a fan of autoboxing in java1.5+ because I thought it got java closer to be truly object-oriented. but, after running into this problem last night, i gotta say that i think this sucks. the compiler giving me an error when I'm trying to do stuff with an uninitialized primitive is a good thing. I dont want to use autoboxing if I lose that.
I think I may be misunderstanding the point of autoboxing, but at the same time I will never accept that a boolean should be able to have 3 values. can anyone explain this? what am i not getting?
Boxed types are reference types, and all reference types, primitive boxes or not, can refer to null. That's why a Boolean can refer to null. So can an Integer. So can a String, etc.
Boxed types are not designed to make Java truly object oriented. Java will never be a purely object oriented language, and you should not code as if this is the case. Primitive types will never go away, and in fact should be preferred whenever there's a choice.
Here's a quote from Effective Java 2nd Edition, Item 49: Prefer primitive types to boxed primitives (emphasis by author):
In summary, use primitives in preference to boxed primitive whenever you have the choice. Primitive types are simpler and faster. If you must use boxed primitives, be careful! Autoboxing reduces the verbosity, but not the danger, of using boxed primitives. When your program compares two boxed primitives with the == operator, it does an identity comparison, which is almost certainly not what you want. When your program does mixed-type computations involving boxed and unboxed primitives, it does unboxing, and when your program does unboxing, it can throw NullPointerException. Finally, when your program boxes primitive values, it can result in costly and unnecessary object creations.
I've seen at least one case where the null value is useful. Lots of data objects in webservices have nullable boolean fields. Sometimes the user neglects to include a value. In this case you want to be able to discern the lack of a value from a default value. Previously, people would write getX, setX, and isXSet() methods, where isXSet returns false until someone calls setX. Now it's possible to make X be a nullable type and it's clear that it wasn't set if getX returns null.
In addition to everything said here, there are cases where you would very much want to have a third value for booleans - the case of an "optional" property.
We usually encounter it with databases, with boolean columns that allow nulls. Without using Booleans, we would need to use two separate variables, one indicating the value and another whether it is valid.
In fact, if you look at the JDBC API, you can see an example of this problem, where columns get a default value if they are null (e.g., a 0 for numeric fields), and then you have to call "wasNull" to check whether it is a true 0 or a fake null!
Your issue is with autounboxing, not autoboxing. I think autounboxing is evil for more significant reasons:
Consider this:
Integer i = new Integer(1);
Integer i2 = new Integer(12);
System.out.println(i == 10 || i != i2);
One == unboxes and the other doesn't.
Unboxing on operators (as opposed to assignments) was a mistake in my view (given the above - it is just not Java). Boxing, however, is very nice.
I think it's more philosophical than technical question. When you transform primitive type to reference type you should be ready that reference types (i.e. objects) are nullable.
You can watch The Billion Dollars Mistake presentation where C.A.R. Hoare says that his introducing null references to oop (Algol 60) was a mistake.
Josh Bloch in Effective Java recommends to prefer primitive types where it's possible. But sometimes you do have to verify you Boolean variable against null.
There is actually no big difference to the days before Java 1.5 - the problem is not the boolean type (it still has two states) but the Boolean wrapper (which always had 3 states. Boolean.TRUE, Boolean.FALSE and null).
Every conversion from a Boolean object to the boolean primitive requires null checks, with or without autoboxing.
Autoboxing automatically transforms data types between intrinsic types and Object types.
Object types for Boolean can be Boolean.TRUE, Boolean.FALSE, or null. That's why you have to deal with the possible 3 values for a boolean.
In databases, it is common to have three states for a boolean type. Consider a record that tracks whether someone has passed a class. There's TRUE, for passing; FALSE for not passing, and NULL for "currently taking the class". Yes, it's odd, but not having a value is inherit in object oriented programming.
I too find autoboxing a bit distasteful, mainly because it is a feature where the compiler adds bytecode to handle the conversion process. In my opinion, this can lead to people forgetting about important details in the conversion process which might be better remembered (such as the null handling in your case). It is useful, but not nearly as useful as most other features of the Java language.
Personally, I wish that the intrinsics were implemented as lightweight objects instead of "built-in" types. There's a lot of times where the hybrid intrinsic / object type system gets in the way. That said, intrinsics were supposed to be there to improve performance, but it seems that if you must do a lot of intrinsic to Object marshalling, you can't enjoy the intrinsic-only performance boost.
It is the problem with autoboxing, just like Integer i = null;. Integer object can be null while a native int cannot be.
It was never intended, with the introduction of autoboxing, that it replace the primitives. In most places primitives are what you want. If you want to start using the reference types because "it got java closer to be truly object-oriented" then that's your call, but as you are discovering, there are disadvantages with that approach. Performance will be another issue.
Autoboxing (and autounboxing) is there to help with the transitions between code that uses primitives (the majority) and the code that has to use reference types (rare). Of the reference types, Boolean is undoubtedly the rarest, since its small number of instances mean it's almost never worth putting in a Collection.
In summary: if the reference types are causing you trouble, don't use them. But don't say 'autoboxing is bad" just because they turned out not to be helpful in your situation.
Mixing the use of primitive data types and their respective wrapper classes, in Java, can lead to a lot of bugs. The following example illustrates the issue:
int i = 4;
...
if (i == 10)
doStuff();
Later on you figure that you want the variable i to be either defined or undefined, so you change the above instantiation to:
Integer i = null;
Now the equality check fails.
Is it good Java practise to always use the primitive wrapper classes? It obviously would get some bugs out of the way early, but what are the downsides to this? Does it impact performance or the application's memory footprint? Are there any sneaky gotchas?
Using the boxed types does have both performance and memory issues.
When doing comparisons (eg (i == 10) ), java has to unbox the type before doing the comparison. Even using i.equals(TEN) uses a method call, which is costlier and (IMO) uglier than the == syntax.
Re memory, the object has to be stored on the heap (which also takes a hit on performance) as well as storing the value itself.
A sneaky gotcha? i.equals(j) when i is null.
I always use the primitives, except when it may be null, but always check for null before comparison in those cases.
Firstly, switching from using a primitive to using an object just to get the ability to set it to null is probably a bad design decision. I often have arguments with my coworkers about whether or not null is a sentinel value, and my opinion is usually that it is not (and thus shouldn't be prohibited like sentinel values should be), but in this particular case you're going out of your way to use it as a sentinel value. Please don't. Create a boolean that indicates whether or not your integer is valid, or create a new type that wraps the boolean and integer together.
Usually, when using newer versions of Java, I find I don't need to explicitly create or cast to the object versions of primitives because of the auto-boxing support that was added some time in 1.5 (maybe 1.5 itself).
I'd suggest using primitives all the time unless you really have the concept of "null".
Yes, the VM does autoboxing and all that now, but it can lead to some really wierd cases where you'll get a null pointer exception at a line of code that you really don't expect, and you have to start doing null checks on every mathematical operation. You also can start getting some non-obvious behaviors if you start mixing types and getting wierd autoboxing behaviors.
For float/doubles you can treat NaN as null, but remember that NaN != NaN so you still need special checks like !Float.isNaN(x).
It would be really nice if there were collections that supported the primitive types instead of having to waste the time/overhead of boxing.
In your example, the if statement will be ok until you go over 127 (as Integer autoboxing will cache values up to 127 and return the same instance for each number up to this value)
So it is worse than you present it...
if( i == 10 )
will work as before, but
if( i == 128 )
will fail. It is for reasons like this that I always explicitly create objects when I need them, and tend to stick to primitive variables if at all possible
Thee java POD types are there for a reason. Besides the overhead, you can't do normal operations with objects. An Integer is an object, which need to be allocated and garbage collected. An int isn't.
If that value can be empty, you may find that in your design you are in need of something else.
There are two possibilities--either the value is just data (the code won't act any differently if it's filled in or not), or it's actually indicating that you have two different types of object here (the code acts differently if there is a value than a null)
If it's just data for display/storage, you might consider using a real DTO--one that doesn't have it as a first-class member at all. Those will generally have a way to check to see if a value has been set or not.
If you check for the null at some point, you may want to be using a subclass because when there is one difference, there are usually more. At least you want a better way to indicate your difference than "if primitiveIntValue == null", that doesn't really mean anything.
Don't switch to non-primitives just to get this facility. Use a boolean to indicate whether the value was set or not. If you don't like that solution and you know that your integers will be in some reasonable limit (or don't care about the occasional failure) use a specific value to indicate 'uninitialized', such as Integer.MIN_VALUE. But that's a much less safe solution than the boolean.
When you got to that 'Later on' point, a little more work needed to be accomplished during the refactoring. Use primitives when possible. (Capital period) Then make POJOs if more functionality is needed. The primitive wrapper classes, in my opinion, are best used for data that needs to travel across the wire, meaning networked apps. Allowing nulls as acceptable values causes headaches as a system 'grows'. To much code wasted, or missed, guarding what should be simple comparisons.