This question already has answers here:
What is the actual memory place for static variables?
(7 answers)
Closed 9 years ago.
Why static variables are directly called without any use of object in java?Are they stored in some different memory location?And why only static methods can called with the name of the class directly without creating its object ?for example
class First
{
public static void ss()
{
System.out.println("This genius will give answer");
}
}
class Second
{
public static void main(String ar[])
{
First.ss();
}
}
Yes static resources belong to the class and not the objects. And are stored in a separate location kind of global location. You can read more here.
As docs says
Every instance of the class shares a class variable, which is in one fixed location in memory.
The Java programming language supports static methods as well as static variables. Static methods, which have the static modifier in their declarations, should be invoked with the class name, without the need for creating an instance of the class, as in
ClassName.methodName(args)
Related
I am currently learning Java and C and get confused with the "static" keyword. In C I mainly use static variables as global variables. In java, I use it for initializing methods eg.
"public static void SomeMethods(){}". also for global variables within classes
eg.
public class ThisClass{
static int var=0;
public static void main(){var++;}
public static void add(){var++}
}
what does static mean and whats the difference in java and C?
The static keyword in Java is used for memory management mainly. We can apply static keyword with variables, methods, blocks and nested classes. The static keyword belongs to the class than an instance of the class.
The static can be:
Variable (also known as a class variable)
Method (also known as a class method)
Block
Nested class.
Variable :-The static variable can be used to refer to the common property of all objects (which is not unique for each object), for example, the company name of employees, college name of students, etc.
The static variable gets memory only once in the class area at the time of class loading.
Method :-A static method belongs to the class rather than the object of a class.
A static method can be invoked without the need for creating an instance of a class.
A static method can access static data member and can change the value of it.
Block :-Is used to initialize the static data member.
It is executed before the main method at the time of classloading.
For C : - check this link https://www.javatpoint.com/static-in-c#:~:text=Static%20is%20a%20keyword%20used,variable%20is%20throughout%20the%20program.
This question already has answers here:
What does the 'static' keyword do in a class?
(22 answers)
Closed 2 years ago.
I've learned that I should use Object(instance) for using instance field in static method.
For example:
INSTANCE FIELD(==speed)
that is declared in public class Car, should be used through Object in static method (ex. 'public static void main(String[] args) )
like this.
Car myCar = new Car();
myCar.speed = 60;
So, the reason I should use object is because static method is located in CLASS and for being shared to objects, but on the other hand, instance field is just Frame that is not substance?
For using this instance field in static method, do I have to make the instance that is called 'object'?
In other words, is this process right?:
instance field -> OBJECT( substantialization) -> static method.
I'm wondering what I understood
static methods are used for 3 reasons:
"stateless" methods. A good example of this would be Math.sin
Global "singletons": singleton is in quotes because the singleton pattern is not used everywhere in java. An example of where it is could be Runtime.getRuntime() an example of where it isn't might be Thread.getUncaughtExceptionHandler (implicit singleton)
Program entry point (public static void main) : It makes sense for a program to start outside of an object context (rather than innside)
Is it bad practice to, in the class which contains the main method, declare all members of that class as static? If so, why? Is it better to, in the main method, create a new instance of the enclosing class, and run the program from the constructor so to speak?
EDIT: (clarification)
I know the concept about static and singletons and generally when to use it. But this question regards specifically the main-class of a program. #Andrew Tobilko (who apparently removed his answer..) seems to have best understood my question judging from his answer. In my case, my main-class is about 200 LOC, and it uses two other small class (< 100 LOC each), so it's a small program. The main-class contains creating a Swing GUI and some running logic, nothing which there needs to be several instances of, so I thought I might just make everything static, to be able to use everything from the static main-method. Is this motivated? A friend who codes in C# told me using a lot of static would mean death penalty in C#. Can there be some memory problems with it or something?
It's not 'better' - it depends on what you need to do.
Declaring all the members of a class as static (including methods) simply turns the class into a singleton. If that's your use-case, then yes.
Declaring an attribute as static means that there is only one copy of this attribute which is shared by all the instances of the class.
If your use-case requires creating multiple instances, and each one of these objects should have its own "private copy" of an attribute then you shouldn't declare that attribute as static.
It's recommended to read more about the topic before you continue implementing.
Static Variables:
The static key word is used to create variables that will exist independently of any instances created for the class. Only one copy of the static variable exists regardless of the number of instances of the class.
Static variables are also known as class variables. Local variables cannot be declared static.
Static Methods:
The static key word is used to create methods that will exist independently of any instances created for the class.
Static methods do not use any instance variables of any object of the class they are defined in. Static methods take all the data from parameters and compute something from those parameters, with no reference to variables.
Class variables and methods can be accessed using the class name followed by a dot and the name of the variable or method.
static modifier are for class members. It should be only used when you want to get a single copy of instance through out the program.
Below is example to explain it,
public class InstanceCounter {
private static int numInstances = 0;
protected static int getCount() {
return numInstances;
}
private static void addInstance() {
numInstances++;
}
InstanceCounter() {
InstanceCounter.addInstance();
}
public static void main(String[] arguments) {
System.out.println("Starting with " +
InstanceCounter.getCount() + " instances");
for (int i = 0; i < 500; ++i){
new InstanceCounter();
}
System.out.println("Created " +
InstanceCounter.getCount() + " instances");
}
}
This would produce the following result:
Started with 0 instances
Created 500 instances
You could check this DuplicateQuestion for your reference
Static entity can give a call to or interact with static entities i.e. a static method can call only a static method or interact with a static variable. That is the property of static methods. Main class in java is mostly declared as "public static void main", which makes main a static method. Hence, the functions it calls are to be static.
Generally class used for constants will hold all final static
variables.
Utility classes holds all static methods.Eg - Math
class in Java
This question already has answers here:
Any risk using a single dollar sign `$` as a java class name?
(5 answers)
Closed 9 years ago.
Is it possible to use functions in Java? I'm not used to OOP and I like having global functions that can be used in any classes. Is this possible in Java? Right now, I have a class named $ that contains all my functions (as static methods). Is there a Java convention for using classes like this? (I borrowed the $ from JQuery)
You can write static class methods with no state, which is effectively a pure function. You can do a "static import" so you don't have to reference the enclosing class. However all your methods/functions must be defined in a class. So, yes, you can do those things, but the syntax isn't perfect.
Java encapsulates everything in classes. You must have all functions within a class. You can either have one big class with many functions and program your Java program more or less like you are writing C or have static functions/class method.
For instance you can have a class Gloabls where you put all your functions:
class Globals {
public static int AddNumbers(int a, int b) { return a+b; }
}
class MyClass {
public MyClass { int four = Globals.AddNumbers(1,3); }
public static void main(String[] args) { new MyClass(); }
}
This question already has answers here:
Difference between static and global variable in Java
(5 answers)
Closed 6 years ago.
I'm so confused by the difference between static variables and the global variables. When I browsing a Java textbook today, my eyes were caught by "Variables declared as static are, essentially, global variables. When an object is declared, no copy of a static variable is made." I am crystal clear about why static variable is shared by all objects in its class, but I don't get why static variables are global variables. In my understanding, the static variables could be only considered as "global" in its class.
Static variables can (and should) be accessed using Class.Variable.
A static variable will always be available globally if they're public.
public class MyClass {
public static int X = 5;
}
Can be accessed everywhere the class is available using
MyClass.X
There's no actual 'global' keyword or anything, but it's close to its intention.
I think your book is (wrongly) using global as an easier way to describe a variable tied to a class.
For instance, take this class:
public class Apple {
private static int numberOfApples = 0;
public Apple() {
numberOfApples++;
System.out.println(numberOfApples);
}
}
Each time an Apple is created it will increment the numberOfApples variable and print it out. If you create two Apple objects then it will print:
1
2
The static variable in this case is globally shared by all Apple instances which may be what it means, but that is because it's tied to the class. This is different than a global variable in other languages.
edit: As others have mentioned, you can access a static variable without any instantiations of the class. If I made numberOfApples public and printed it out before creating any Apple instances then it would print 0. Similarly, after creating two Apple classes and then having both objects be destroyed, I could print numberOfApples and it would say 2.
Static: there exists exactly one variable with that name. (while instance variables exist for every instance)
Global: Static and visibility is public.
Hence, every global variabel must be static.
Example of a global variable is: java.lang.System.out
What's the difference between the static variable and the global variable (Java)?
The difference is that global variables don't exist in Java. Your book shouldn't even have mentioned them.
As far as i Know, memory is allocated by object which is declared in main which calls the method. If it invokes a non-static variable, then it is initialized everytime it is invoked. On the other hand, memory is allocated for static variable once only then whenever it is called it's value remains same.