Any kind of data your computer stores and processes is in its most basic representation a row of bits. The way those bits are interpreted is done through data types. Data types can be primitive or complex. Primitive data types are – for instance – int or double. They have a specific length and a specific way of being interpreted. In the case of an integer, usually the first bit is used for the sign, the others are used for the value.
Complex data types can be combinations of primitive and other complex data types and are called “Class” in Java.
You can define the complex data type PeopleName consisting of two Strings called first and last name. Each String in Java is another complex data type. Strings in return are (probably) implemented using the primitive data type char for which Java knows how many bits they take to store and how to interpret them.
When you create an instance of a data type, you get an object and your computers reserves some memory for it and remembers its location and the name of that instance. An instance of PeopleName in memory will take up the space of the two String variables plus a bit more for bookkeeping. An integer takes up 32 bits in Java.
Complex data types can have methods assigned to them. Methods can perform actions on their arguments or on the instance of the data type you call this method from. If you have two instances of PeopleName called p1 and p2 and you call a method p1.getFirstName(), it usually returns the first name of the first person but not the second person’s.
