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If you are a Salesforce developer, you need to know everything about static and instance in Apex Salesforce to code as a pro with good programming principles.

In apex classes can’t be static. Nonetheless, we can have static methods, variables and initialization code. Also we can have instance methods, member variables and initialization code, which have no modifier, and local variables.

Static Characteristics in Apex

Static methods, variables and initialization code could be:

  • Associated with a class.
  • Only in outer classes.
  • Only when a class is loaded.
  • No transmitted as part of the view state for a Visualforce page.

Instance Characteristics in Apex

Instance methods, member variables, and initialization code could be:

  • Associated with a particular object.
  • No definition modifier.
  • Created with every object instantied from the class declared.

Using Static Methods and Variables

  • Only with outer classes. That means, classes that can have inner classes.
  • Doesn’t require an instance of the class in order to run.
  • All static variables are initialized before an object of a class is created.
  • A static method is used as a utility method. For example, when we need to access to raw data without make an object declaration.
  • A static variable is static only within the scope of the Apex transaction. Can be used as a flags in Apex Triggers.
  • A static variable or method can’t be accessed through an instance of that class.
  • An inner class behaves like a static class and doesn’t require the static keyword. Those classes doesn’t need to be declared.
  • In other words, use static methods and variables when you don’t need the abstraction of an object but straight code.
  • Ask yourself “Does it make sense to call this method, even if no object has been constructed yet?” If so, it should definitely be static.
public class P { 
   public static boolean firstRun = true; 
}
trigger T1 on Account (before delete, after delete, after undelete) { 
  if(Trigger.isBefore){
    if(Trigger.isDelete){
        if(p.firstRun){
            Trigger.old[0].addError('Before Account Delete Error');
            p.firstRun=false;
        } 
      }
  }
}

Using Instance Methods and Variables

  • Are used by instance of a class, that is, by an object.
  • Instance member variable is declared inside a class.
  • Usually use instance member variables to affect the behavior of the method.
  • In other words, use it when depends of an object and could affect their behaviour. For example, a Point, need an instance of x and y to be created.
public class Plotter {
 
    // This inner class manages the points
    class Point {
        Double x;
        Double y;
 
        Point(Double x, Double y) {
             this.x = x;
             this.y = y;
        }
        Double getXCoordinate() {
             return x;
        }
 
        Double getYCoordinate() {
             return y;
        }
    }
 
    List<Point> points = new List<Point>();
 
    public void plot(Double x, Double y) {
        points.add(new Point(x, y));
    }
    
    // The following method takes the list of points and does something with them
    public void render() {
    }
}

References

To learn more about Salesforce can see: The Lightning Component Framework

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