Week 4: Writing classes/02A Objects' methods

Once an object has been created by calling a constructor, the information content of the object 
can be observed and modified through the public OPERATIONS it provides. 
For example, as we know, a list has a public method add, which can be used to add an element to the list:

ArrayList<Double> measurements = new ArrayList<>();
measurements.add(2.5);
measurements.add(14.0);
measurements.add(-2.75);

System.out.println(measurements);
 
Program outputs:
[2.5, 14.0, -2.75]
 
 




Changing the data content of one object does not change the data content of other objects of the same class.
Objects are therefore INDEPENDENT ENTITIES. 
When we add one element to a list, the other lists of the same class do not change.

ArrayList<Double> measurements1 = new ArrayList<>();
ArrayList<Double> measurements2 = new ArrayList<>();

measurements1.add(2.5);
measurements1.add(14.0);
measurements1.add(-2.75);

measurements2.add(0.25);
measurements2.add(0.75);

System.out.println(measurements1);
System.out.println(measurements2);
 

Program outputs:
[2.5, 14.0, -2.75]
[0.25, 0.75]