Non static method cannot be referenced from a static context

[Rebecca Witmer]

I have this code in my program:

public Vector sort(Vector averages) {
//put in TreeMap
TreeMap sortedMap = new TreeMap();
for (int l = 0; l < averages.size(); l++) {
Double element = (Double) averages.elementAt(l);
Integer index = new Integer(l);
TreeMap.put(element, index);
}

but JBuilder highlights "put" and says, "Non static method cannot be referenced from a static context". What's it talking about?

[Jayesh Lalwani]

shouldnt that be sortedMap.put ?

[Rebecca Witmer]

Doh!

[C. Magmanum]

as u know, most java programs start at main and the syntax for the main method is

public static void main(String args[]){}

it is a static method and it can only make calls to static codes. Make sure the object u want to use is istantiated in your main method and also make sure that u import the java.util.*

I hope it solves your problem, I'm a novice too

[Amit Saini]

Hi Rebecca,
Think of 'static' as 'one per class'.
Static methods and variables are initialized when the class is loaded.
Since static variables and methods dont belong to any object, you cant call them as 'objectName.methodName' or 'objectName.variableName'. You have to prefix the class name like,
className.methodName' or 'className.variableName'

In your case, you're doing TreeMap.put, but does the put() method belong to the TreeMap class or the TreeMap object? If TreeMap was a static class, then your syntax would make sense. However, it is not, so you need to access the put() method with an object of TreeMap.

Hope that helps !