Encapsulation is used to hide the values or state of a structured data object inside a class, preventing unauthorized parties' direct access to them. For example, in the coinpurse lab we try to encapsulate the Purse class and it related class so that when we modify we don't have to make many collection in input and output logic(ConsoleDialog).
//In ConsoleDialog class
Valuable[] valuable = purse.withdraw(amount);From the example above, ConsoleDialog doesn't know how Purse class work. And even if we modify how we perform the withdrawal inside the Purse class (such as the withdrawal algorithm), we don't have to make any changes in the ConsoleDialog.
Exercise : Click Here
References : http://principles-wiki.net/principles:encapsulate_the_concept_that_varies
LSP or Liskov Substitution Principle is a principle in OOP. It explains that "functions that use references to the base classes must be able to use objects of derived class without knowing it". In simple words, any subclass must be able to substitute its parent class perfectly. For example, Student, inheriting from Person, must be able to do everything that Student can do.
Person person = new Person("foo");
Person student = new Student("foo");
// Result must be true!
person.getName().equals(student.getName());From the example above, when Student is being known as a Person (substituting), Person it must be able to do whatever Person can do too.
Exercise : Click Here
References : http://vitalflux.com/liskov-substitution-principle-with-java-code-examples/