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Today, in the Java Developers Group in LinkedIn; I found this question posted by Sneha Kesri. She asked “What is the size of ” null ” Operator in Java ?”.
Actually, I never thought of it that way, but I continued reading.
from the heap memory perspective it will be 0, as it wont allocate any memory from heap. But from stack memory perspective the object has reference which is set to null. and the reference variable size depends your system.
for 32 bit system it will be 4 byte and for 64 bit system it will be 8 byte.but as such null is not referring to any data from heap, so heap memory will be same.
And that was the only reply by then, which was correct, but Sneha Kesri asked another question:
Thanks Ramesh, I am having one more doubt… when we say..
String str1 = null; String str2 ="";
So, I replied her with the following :
You create a reference “str1” to an object that still does not exist in the heap, but when you type :
You create a reference “str2” to a string object that is already allocated in the heap which preserves the string object size.
if you do that expression
It should evaluate to false, because you are comparing reference values, which will not be equal.
if you do that expression
It should throw a NullPointerException because you are trying to access the method equals on a null object ( str1 )
but if you try that expression
It should return false, because the value of ( str2 ) is an empty string not null object.
Does null variable consume memory
posted 4 years ago
I’ve been browsing over stackoverflow and came across with an answer where a guy shared that every null variable within a class will consume 8 bytes(64 bit)/4 bytes (32 bit) while instantiate it. Below is the quoted answer :
«In Java, null is just a value that a reference (which is basically a restricted pointer) can have. It means that the reference refers to nothing. In this case you still consume the space for the reference. This is 4 bytes on 32-bit systems or 8 bytes on 64-bit systems. However, you’re not consuming any space for the class that the reference points to until you actually allocate an instance of that class to point the reference at.
Edit: As far as the String, a String in Java takes 16 bits (2 bytes) for each character, plus a small amount of book-keeping overhead, which is probably undocumented and implementation specific.»
So, I am bit confused why we assign null to any variable or reference to make it available for GC.
Saloon Keeper
posted 4 years ago
I think it’s a bit silly to say that null takes up memory. There are only two things that take up memory: Variables and objects.
Variables of a reference type take up 32 bits on a 32 bit system, and 64 bits on a 64 bit system, regardless of their value. If you declare an extra local variable of a reference type, the stack frame grows by 4 bytes on a 32 bit system. If you declare an extra field of a reference type, instances of the declaring class will grow by 4 bytes on a 32 bit system.
You don’t assign null to variables to make «it» available for GC. First of all, what is «it»?
Objects are eligible for garbage collection when there are no variables that hold a reference to them, or if the only things that hold a reference to them are instance fields that belong to objects that themselves are eligible for garbage collection. Most of the time, this happens correctly without you having to help the garbage collector. Only in very special cases do you assign null to a field or array element to help the garbage collector determine that an object is no longer used.
Remember that garbage collection is not about clearing the values of fields, it’s about removing unused objects from memory.
What Is the null Type in Java?
The Kubernetes ecosystem is huge and quite complex, so it’s easy to forget about costs when trying out all of the exciting tools.
To avoid overspending on your Kubernetes cluster, definitely have a look at the free K8s cost monitoring tool from the automation platform CAST AI. You can view your costs in real time, allocate them, calculate burn rates for projects, spot anomalies or spikes, and get insightful reports you can share with your team.
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We rely on other people’s code in our own work. Every day.
It might be the language you’re writing in, the framework you’re building on, or some esoteric piece of software that does one thing so well you never found the need to implement it yourself.
The problem is, of course, when things fall apart in production — debugging the implementation of a 3rd party library you have no intimate knowledge of is, to say the least, tricky.
Lightrun is a new kind of debugger.
It’s one geared specifically towards real-life production environments. Using Lightrun, you can drill down into running applications, including 3rd party dependencies, with real-time logs, snapshots, and metrics.
Learn more in this quick, 5-minute Lightrun tutorial:
Slow MySQL query performance is all too common. Of course it is. A good way to go is, naturally, a dedicated profiler that actually understands the ins and outs of MySQL.
The Jet Profiler was built for MySQL only, so it can do things like real-time query performance, focus on most used tables or most frequent queries, quickly identify performance issues and basically help you optimize your queries.
Critically, it has very minimal impact on your server’s performance, with most of the profiling work done separately — so it needs no server changes, agents or separate services.
Basically, you install the desktop application, connect to your MySQL server, hit the record button, and you’ll have results within minutes:
DbSchema is a super-flexible database designer, which can take you from designing the DB with your team all the way to safely deploying the schema.
The way it does all of that is by using a design model, a database-independent image of the schema, which can be shared in a team using GIT and compared or deployed on to any database.
And, of course, it can be heavily visual, allowing you to interact with the database using diagrams, visually compose queries, explore the data, generate random data, import data or build HTML5 database reports.
The Kubernetes ecosystem is huge and quite complex, so it’s easy to forget about costs when trying out all of the exciting tools.
To avoid overspending on your Kubernetes cluster, definitely have a look at the free K8s cost monitoring tool from the automation platform CAST AI. You can view your costs in real time, allocate them, calculate burn rates for projects, spot anomalies or spikes, and get insightful reports you can share with your team.
Connect your cluster and start monitoring your K8s costs right away:
We’re looking for a new Java technical editor to help review new articles for the site.
1. Introduction
In the world of Java, the null type is pervasive, and it’s hard to use the language without encountering it. In most cases, the intuitive understanding that it represents nothingness or lack of something suffices to program effectively. Nevertheless, sometimes we want to dig deeper and thoroughly understand the topic.
In this tutorial, we’ll look at how the null type works under the hood and how it relates to other types.
2. What Is a Type?
Before we answer the specific question about the null type, we need to define what a type really is. This isn’t an easy task because there are a lot of competing definitions. The one that will be the most useful to us is the definition of value space. In that definition, a type is defined by the set of possible values it can hold.
Let’s say we want to declare a boolean variable:
What we’ve done is declare that the variable named “valid” will hold one of two possible values: true or false. The set of possible values has only two elements. If we want to declare an int variable, the set of possible values would be much larger but still clearly defined: every possible number from -2^31 to 2^31-1.
3. What Type Is null?
null is a special type that has only one possible value. In other words, the set of possible values has only one element. This characteristic alone makes the null type very peculiar. Normally, the whole purpose of variables is that they can assume different values. There’s only one null reference, so a variable of the null type could only hold that one specific reference. It would bring no information apart from that the variable exists.
There’s one trait that makes the null type usable in the way we use it. The null reference can be cast to any other reference type. That means we can treat it like a special literal, which can be of any non-primitive type. In practice, the null reference extends the effective set of possible values of these types.
That explains why we can assign the exact same null reference to variables of totally different reference types:
Integer age = null; List names = null;That also explains why we can’t assign the null value to variables of primitive types like boolean:
Boolean validReference = null // this works fine boolean validPrimitive = null // this does notIt’s because the null reference can be cast to a reference type but not to a primitive one. The set of possible values of a boolean variable will always have two elements.
4. null as a Method Parameter
Let’s take a look at two simple methods, both taking one parameter but of different types:
void printMe(Integer number) < System.out.println(number); >void printMe(String string)
Because of polymorphism in Java, we can call these methods like this:
The compiler will understand what method we’re referencing. But the following statement will cause a compiler error:
printMe(null); // does not compileWhy? Because null can be cast to both String and Integer – the compiler won’t know which method to choose.
5. NullPointerException
As we’ve seen already, we can assign the null reference to a variable of a reference type even though null is technically a different, separate type. If we try to use some property of that variable as if it wasn’t null, we’ll get a runtime exception – NullPointerException. It happens because the null reference isn’t the type we’re referencing it to be and doesn’t have the properties we expect it to have:
String name = null; name.toLowerCase(); // will cause exception at runtimeBefore Java 14, NullPointerExceptions were short, simply stating in which line of the code the error happened. If the line was complex and had a chain of invocations, that information wasn’t informative. However, from Java 14, we can rely on so-called Helpful NullPointerExceptions.
6. Conclusion
In this article, we looked closely at how the null type works. First, we defined a type, and then we found how the null type fits into that definition. Finally, we learned about how a null reference can be cast to any other reference type, making it the tool that we know and use.
Slow MySQL query performance is all too common. Of course it is. A good way to go is, naturally, a dedicated profiler that actually understands the ins and outs of MySQL.
The Jet Profiler was built for MySQL only, so it can do things like real-time query performance, focus on most used tables or most frequent queries, quickly identify performance issues and basically help you optimize your queries.
Critically, it has very minimal impact on your server’s performance, with most of the profiling work done separately — so it needs no server changes, agents or separate services.
Basically, you install the desktop application, connect to your MySQL server, hit the record button, and you’ll have results within minutes: