Notes for Engineers

Basic Java Concepts

• A class should represent a single concept from the problem domain, such as business, science, or mathematics.
  
• The public interface of a class is cohesive if all of its features are related to the concept that the class represents.
  
• A class depends on another class if it uses objects of that class.
  
• It is a good practice to minimize the coupling/dependency between classes.
  
• An immutable class has no mutator methods.
  
• A side effect of a method is any externally observable data modification.
  
• You should minimize side effects that go beyond modification of the implicit parameter.
  
• In Java, a method can never change parameters of primitive type.
  
• In Java, a method can change the state of an object reference parameter, but it cannot replace the object reference with another.
  
• A precondition is a requirement that the caller of a method must meet. If a method is called in violation of a precondition, the method is not responsible for computing the correct result.
  
• An assertion is a logical condition in a program that you believe to be true.
  
• If a method has been called in accordance with its preconditions, then it must ensure that its post-conditions are valid.
  
• A static method is not invoked on an object.
  
• A static field belongs to the class, not to any object of the class.
  
• The scope of a variable is the region of a program in which the variable can be accessed.
  
• The scope of a local variable cannot contain the definition of another variable with the same name.
  
• A qualified name is prefixed by its class name or by an object reference, such as Math.sqrt or other.balance.
  
• An unqualified instance field or method name refers to the 'this' parameter.
  
• A local variable can shadow a field with the same name. You can access the shadowed field name by qualifying it with the 'this' reference'.
  
• A package is a set of related classes.
  
• The 'import' directive lets you refer to a class of a package by its class name, without the package prefix.
  
• Use a domain name in reverse to construct unambiguous package names.
  
• The path of a class file must match its package name.
  
• Unit test frameworks simplify the task of writing classes that contain many test cases. The JUnit philosophy is to run all tests whenever you change your code.
  
• Mutator methods modify the object on which it is invoked
  
• Accessor method accesses info without making any mods.
  
• Always get the same answer, unlimited, and state of object does not change.
  
• Immutable methods have only accessor and not mutator
  
• Safe to give out references to its objects freely
  
• Once a string is constructed, its contents never change.