Solved it, but didn't quite understand

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Hi! Why "public int C = A * B;" (non static) can use "A" and "B" (which are static)? Inside this static and non static field, what's the difference between "public int C = A * B;" and "public static int D = B * A;"? I've already read the article about it, but everytime this task appears I see that I didn't really get it...

public static int A = 5;
public static int B = 2;

public int C = A * B;
public static int D = B * A;

Thanks!

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Gellert Varga

Level 23 , Szekesfehervar, Hungary

14 May 2020, 22:00

useful

Hi again:) Let's start a little bit clarifying. Which modifier means exactly what? public class Cat int age; String name; static int count; 1) "static". (variable 'count'). This means: this variable (or a static method) belongs only to its own class. It doesn't belong to any object. Other name: class-variable, class-method. You can create objects from the class Cat, but the static 'count' variable is not the part of any cat-object! 2) "non-static": (age, name): these variables belongs only to the Cat-objects. Other name: instance-variable, instance-method. (instance means: object!) If you don't create any Cat-object, then these variables don't even exist!! If doesn't exist any Cat-object, then you can't use these variables. (The same applies to non-static methods too.) No one can do anything with these variables (methods). Only the created objects can do something with them! The nonstatic variables and methods are just a pattern for future objects. The first existing thing is static: The JVM starts the program run with the STATIC main method. This static main method (and all the other static method) can access/call/run only the static variables and static methods. They can not access the non-static variables or non-static methods! The non-static variables and methods are accessable only by objects. After if you create an object in the static main method. (Or, the static main method calls an other static method, and you will create an object inside this static method.) Non-static (instance)methods/variables can use the static (class)variables/methods! But static (class)methods/variables can not use the non-static variables/methods! When the program use the class Cat at first time, the static count variable will be inicialized to zero (zero is the default value.) The nonstatic (instance)variables (age,name) will be inicialized only if you create a Cat-object! It was some general explaining. If you have questions,feel free to ask!

Gellert Varga

Level 23 , Szekesfehervar, Hungary

14 May 2020, 22:06

useful

And now this is about the specific task. (See also the attached screenshot!) Line 14: the getValue() is static. It can only access static variables. So, 'D' have to be static too! Line 9: static D = B * A; but if 'D' is static, it can only access static variables, so 'A' and 'B' also have to be static! Line 6: 'B' is static, all right. Line 5: 'A' is not static! Let's correct it. Write there: 'static'. Line 18: getValue2() is a nonstatic method. So the variable 'C' can be both static and non-static. Line 8: 'C' is nonstatic. Good. It can use static variables and nonstatic variables too. So, 'A' and 'B': all right! Try this program. The compiler won't indicate any error, so the program is correct! (Always try your programs a lot of times, and monitor/observe its behaviour!) But this way now we have five pieces 'static' modifier... and this doesn't comply with the requirements ("The class must have 4 static modifiers"). So, we have to find other solution, we have to go in other direction. But now, after all this, i think You also are able can do it:)

Henrique

Level 41 , São Paulo, Brazil

15 May 2020, 13:03

Hey! Thanks for your time answering to me! As I said, I had already solved the problem, but I asked this question here because I solved it without fully understanding it. My lack of understanding was basically about what you described is these two sentences: "Non-static (instance)methods/variables can use the static (class)variables/methods!" "But static (class)methods/variables can not use the non-static variables/methods!" With that, I was able to understand much more! But I'll have to read again and again everything you wrote, for me to comprehend even more. Thanks again!

Gellert Varga

Level 23 , Szekesfehervar, Hungary

15 May 2020, 20:02

All right. Use it with health:) (At first, I also had a hard time to understand this topic. From crumbs of informations, from the right and from the left, and to put them into a whole thing. My hope is i didn't misunderstood anything...)

sourav bamotra

Level 20 , jammu, India

14 August 2020, 15:19

good explanation ....i will be looking forward to you. :)

Ashish RajAnand

Level 13 , Bhilai , India

14 May 2020, 02:09

Point 1-static depend on it datatype that you defined. ex

public static int A=5;//this is static variable
public int C=A*B; //this is not static variable because we didn't define it with static .

Here is your point ,

=   //assignment operator work simply store the value from right to left in container at left side .

It only use its values . So when we use static variable doesn't mean left side variable is also the static .