Java – static concepts

javastatic

class Trial 
{   static int i; 
    int getI() 
    {       return i;} 
    void setI(int value) 
    {       i = value;} 
} 
public class ttest 
{  public static void main(String args[]) 
   {    Trial t1 = new Trial(); 
        t1.setI(10); 
        System.out.println(t1.getI()); 
        Trial t2 = new Trial(); 
        t2.setI(100); 
        System.out.println(t1.getI()); 
        System.out.println(t2.getI()); 
   } 
}

Here trial is a non static class and i is a static variable. How can I access this from a static main method. Is this way correct?

Best Solution

Yes it's the correct way.

When a class is not static you need to instance it with new keyword. Like you did

Trial t1 = new Trial();

The static variable i shouldn't be static if you do not want to share its value between all Trial object. If you want to use this value (in "sharing mode") you can do it the way you did it. If you put this variable public you could simply do Trial.i = "your value"...

Related Solutions

Python – Are static class variables possible in Python

Variables declared inside the class definition, but not inside a method are class or static variables:

>>> class MyClass:
...     i = 3
...
>>> MyClass.i
3

As @millerdev points out, this creates a class-level i variable, but this is distinct from any instance-level i variable, so you could have

>>> m = MyClass()
>>> m.i = 4
>>> MyClass.i, m.i
>>> (3, 4)

This is different from C++ and Java, but not so different from C#, where a static member can't be accessed using a reference to an instance.

See what the Python tutorial has to say on the subject of classes and class objects.

@Steve Johnson has already answered regarding static methods, also documented under "Built-in Functions" in the Python Library Reference.

class C:
    @staticmethod
    def f(arg1, arg2, ...): ...

@beidy recommends classmethods over staticmethod, as the method then receives the class type as the first argument, but I'm still a little fuzzy on the advantages of this approach over staticmethod. If you are too, then it probably doesn't matter.

Java inner class and static nested class

From the Java Tutorial:

Nested classes are divided into two categories: static and non-static. Nested classes that are declared static are simply called static nested classes. Non-static nested classes are called inner classes.

Static nested classes are accessed using the enclosing class name:

OuterClass.StaticNestedClass

For example, to create an object for the static nested class, use this syntax:

OuterClass.StaticNestedClass nestedObject = new OuterClass.StaticNestedClass();

Objects that are instances of an inner class exist within an instance of the outer class. Consider the following classes:

class OuterClass {
    ...
    class InnerClass {
        ...
    }
}

An instance of InnerClass can exist only within an instance of OuterClass and has direct access to the methods and fields of its enclosing instance.

To instantiate an inner class, you must first instantiate the outer class. Then, create the inner object within the outer object with this syntax:

OuterClass outerObject = new OuterClass()
OuterClass.InnerClass innerObject = outerObject.new InnerClass();

see: Java Tutorial - Nested Classes

For completeness note that there is also such a thing as an inner class without an enclosing instance:

class A {
  int t() { return 1; }
  static A a =  new A() { int t() { return 2; } };
}

Here, new A() { ... } is an inner class defined in a static context and does not have an enclosing instance.

Best Solution

Related Solutions

Python – Are static class variables possible in Python

Java inner class and static nested class

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