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What does the 'static' keyword do in a class?
(22 answers)
Difference between Static and final?
(11 answers)
Closed 2 years ago.
I am confused about when to use Static variables/methods and exactly what they do. I know Static means that the variable or method becomes a part of the class and not an instance, but when do we use this? Also, if a variable is static, does that mean it is immutable like a final variable? Basically what is the use of Static?
You will usually use static when your variables are general and are not supposed to be part of each instance separately, take as an example the number pi, if you create a Math class, you will set pi as a static final variable, and also the methods will be declared as static, because you don't want to create a class instance everytime you want to use the power function. If your function doesn't use the properties of the class it will probably be static.
Another use I found useful, when you create a class within another, you should declare the inner class as static, otherwise you will need an instance to create instance of the inner class
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This question already has answers here:
What is "static"?
(7 answers)
What does the 'static' keyword do in a class?
(22 answers)
Closed 9 months ago.
In Java we can use
non-static variables inside non-static methods without creating an
instance within the same class.
static variables inside non-static methods without having an issue within the same class.
static variables inside a static a static method without having any issue within the same class.
I just want to know why we can not use a non static variable inside a static method within the same class.
It wouldn't make sense. Static methods are about belonging to the class, rather than individual instances. So, they don't have access to any instance (i.e. you can't use this™ inside them).
Things that aren't static are bound to individual instances.
This question already has answers here:
When are static variables initialized?
(7 answers)
Closed 7 years ago.
In Java I've always seen Class variables (defined with keyword static) as equivalent of global variables in other languages such as C, defined inside a class to avoid name conflicts. In C you can refer a global variable from any function at any time it always exists while the program is running.
What about static variables in Java. Do they always exist? Do they always get loaded when they're referred? I wanna know if it's always safe when I use a static variable from a static method of another class.
Also does a static variable ever get destroyed?
A static variable is initialized when the class is initialized, and so will always be valid (Initialization of Classes and Interfaces).
Initialization of a class consists of executing its static initializers and the initializers for static fields (class variables) declared in the class.
If the value of the static field is changed, and there are no other references to the previous value, then the previous value will be garbage collected. However, the reference itself will always exist, so if "safe" means "never access illegal memory", it is always safe (when using the Java language in general, not just in this case).
This question already has answers here:
Why are interface variables static and final by default?
(16 answers)
Closed 8 years ago.
I am new to Java. I heard that Interface can have only static variables, is that correct?
Yes, because interfaces cannot be instantiated, so instance state would not make sense.
A quick Google search found the same answer.
http://www.coderanch.com/t/245071/java-programmer-SCJP/certification/final-member-variables-interfaces
This is correct. The reason is that Java interfaces cannot be instantiated by themselves. You must instantiate an instance of a class that implements the interface. Because of this, the value of the variables must be assigned in static context because in this case no instance will exist.
They also need to be declared as final to ensure that the value assigned to the interface variable is a true constant that cannot be changed at run-time by other program code.
As mentioned in the comment
public static final variables
1. Interface variables are static because Java interfaces cannot be instantiated in their own right; the value of the variable must be assigned in a static context in which no instance exists.
2. The final modifier ensures the value assigned to the interface variable is a true constant that cannot be re-assigned by program code.
This question already has answers here:
What is the reason behind "non-static method cannot be referenced from a static context"? [duplicate]
(13 answers)
Closed 8 years ago.
I have learned that fields are like global variables which can be accessed by the methods inside the same class. I have done it this way before and never had a problem. I have now a class where I have some fields but the methods cannot access them without having to make them static fields. I get the error "cannot make static reference to non-static..."
I thought static was to access fields on other classes without having to create an object reference to the class. The only difference I have with this code is that I have a single class and my main() method within this class. Does having main() inside this class make a difference?
A static member only exists once for the class itself as opposed to regular class members which are distinct per instance of your class.
Having a main() method does not impact the behavior of your static members, however static methods can only access static members while non-static methods can access both static and non-static class members.
You can't access non static instance inside static method. I think you are trying to access class variable inside main method directly, i.e.
class A
{
int x;
main() method
{
x;//Not accessible here,, create instance of class and access it.like
A a=new A();
a.x;
}
}
Static (methods,variables,classes, etc) belongs to Class not to the particular instance of the class. We define as static when the behaviour or state does not depend on any particular instance of the class. For Example "generate a Random Number " it does not depend on the instance, it always generate a number regardless of instance such behaviour can be defined as static.
Regarding the error, posting you code will helpful to give better solution.
Refer the below link to know more about Static and non-static
http://javarevisited.blogspot.in/2012/02/why-non-static-variable-cannot-be.html
This question already has answers here:
When to use static methods
(24 answers)
Closed 9 years ago.
Specifically using Java. What makes a function static? what does that mean? How should you choose to make the function static or not?
My while loop is broken because "non-static method hasPrecedence(java.lang.String,java.lang.String) cannot be referenced from a static context"
A static method is called outside of a specific instance of a class. For example, in the Java library, the Math.sqrt() function is not associated with a particular object.
In contrast, non-static methods must be called with a specific object. For example, a toUpperCase() method is defined for String objects:
String str = "Hello World.";
String upperStr = str.toUpperCase();
System.out.println(upperStr);
Notice that instead of calling String.toUpperCase() I used str.toUpperCase().
A static method is called outside of any specific object. A non-static method is called with a specific object to operate on.
A function is static if there is only one shared among all instances of a class. Generally, a static function is used for "utility" work. By this I mean, the function does some work for you that does not/should not require making an instance of the class. A static function therefore does not make use of or have access to instance variables or instance methods.