non-static method can not be referenced from a static context

[oll3i]

public IBagResult cartesianProduct(IAbstractQueryResult resLeft, 
         IAbstractQueryResult  resRight){
 
         method inside
          }   
         }

IBagResult commaRes = QExecUtils.cartesianProduct(resLeft, resRight);
qres.push(commaRes);

non-static method can not be referenced from a static context

[chaarmann]

You must declare your method "cartesianProduct" static, if you call it with "QExecUtils.cartesianProduct(...)".
Otherwise, if you want to keep this method non-static, call it by making a new instance of the class:

qExecUtilsInstance= new QExecUtils();
IBagResult result = qExecUtilsInstance.cartesianProduct(...);

[Nepomuk]

Your error message can be explained as follows:

In Java, functions, fields and inner classes can be static if they use the modifier static. These functions / fields / classes do then not belong to an instance of the wrapping class but rather to the outer class itself. Let me give you an example:

public class Example {
    public static void sayHelloStatic() {
        System.out.println("Hello!");
    }
 
    public void sayHelloNonStatic() {
        System.out.println("Hello!");
    }
}

Now you can use those methods like so:

//...
Example.sayHelloStatic();
//...
Example ex = new Example();
ex.sayHelloNonStatic();
//...

You see, for the second one you need an instance of that class while you don't for the first.

The error you're getting occurs when you are trying to call a non-static function from a static one without creating an instance of that object to use it from. This quite often happens in the main function (which is static). So the solution would be

• to create an instance of the object and use the function from there or
• make the function static

In many cases the first solution is to be preferred but there can be very good reasons to go with the second one too.

[oll3i]

ok ... but i have a static method with non-static variables ?

 public static IBagResult ccccc(IAbstractQueryResult resLeft, 
         IAbstractQueryResult  resRight){
     this.resRight = (List)resRight;
     this.resLeft = (List)resLeft;
 for(int i=0; i<=this.resLeft.size(); i++){
 
     for(int j=0; j<= this.resRight.size(); j++) {
         elements.addElements((Integer)this.resLeft.get(i)*(Integer)this.resRight.get(j));
     }   
         }
 return elements;
 
 }

says that non-static variables can not be referenced from a satic context

[Nepomuk]

Correct. The this operator is trying to access an instance of the class. As you're using a static function there is no instance to access.

In this case I'd think you don't want your function to be static.

[oll3i]

i dont even know how to thank You thank You