How to Program with Java Podcast (Trevor Page)

How to Program with Java Podcast
Trevor Page: Java Guru | Programmer | Teacher

Methods

• Short: Methods should perform a single task with no side effects.
• Assigned to a Class: Methods are associated with a class (an object).
• Return vs Void: Methods can either return a value or be void.
• Parameter vs Argument:
  • Parameter: A variable in the method’s signature (method declaration).
  • Argument: An expression used when calling the method.

Arrays

• Arrays have a defined size when created.
• ArrayList is often preferred.

Primitives

• Building blocks with no objects.
• More efficient than objects.
• Examples: int, double, boolean, float, char, byte.
• No reference, no pointer.
• Default values for instance variables.

Objects

• Everything in Java is an object.
• The Object class is the parent class of all classes in Java.
• Useful for referring to objects when their type is unknown.
• Example:
  Object obj = getObject(); // Referring to an object with an unknown type


Static Keyword

• Used for memory management, shared variables, or methods.
• Applies to variables, methods, blocks, and nested classes.
• Belongs to the class rather than an instance.

Inheritance

• Attributes and methods can be inherited from one class to another.
• Categories:
  • Subclass (Child): Inherits from another class.
  • Superclass (Parent): The class being inherited from.
• To inherit from a class, use the extends keyword.
• Interface:
  • Defines an abstract type specifying class behavior.
  • Contains static constants and abstract methods.
• Abstract Class:
  • Important observations:
    • No instance of an abstract class can be created.
    • Constructors are allowed.
    • Can have a final method, but no abstract method in a final class.
    • Cannot create an object for an abstract class.
    • Can define static methods.
    • Abstract keyword can be used for top-level and inner classes.
    • If a class has at least one abstract method, declare the class as abstract.
    • If a child class can’t provide implementation for all abstract methods, declare it as abstract.

Exceptions

• try, catch, finally.
• Checked exceptions are caught at compile time, while unchecked exceptions are at runtime.
• Checked exceptions must be handled, either by re-throwing or using a try-catch block.

Collections

• Data structures: ArrayList, LinkedList, Set, Map.

Packages

• Organizational structure of an app.
• Naming convention: Lowercase and hyphen, e.g., at.ercode.

Constructors

• Special methods used to initialize objects.
• Called when an object of a class is created.
• Sets initial values for object attributes.

Custom Sorting

• Interface – Comparable: Defines compareTo(obj1) method.
• Interface – Comparator: Defines compare(obj1, obj2) method.

Casting

• Down-casting: Parent to child (may cause errors).
• Up-casting: Child to parent.
• Method: instanceOf checks if casting is possible.

Unit-Tests/Mocking

• Arrange, Act, Assert.
• Dependencies should be mocked up.

Interview Questions

• JDK vs JRE.
• Checked vs unchecked exceptions.
• Final vs finally vs finalize.
• Inner class vs subclass.
• Access specifiers/modifiers: public, private, package, protected.
• Data encapsulation.
• Singleton class.
• Continue vs break.
• Java packages.
• Interface vs abstract class.
• HashMap vs Hashtable (synchronized).
• Vector (synchronized) vs ArrayList.

Stream

• Fancy for loop.
• Intermediate operations: filter, map, sorted.
• Terminal operations: collect, forEach, reduce.
• A stream is not a data structure; it processes input from Collections, Arrays, or I/O channels.
• Streams don’t change the original data structure; they provide results as per pipelined methods.
• Each intermediate operation is lazily executed.

Lambda

• A new feature in Java SE 8 for representing one-method interfaces concisely.
• Components: Argument-list, Arrow-token, Body.
• Useful in the collection library for iterating, filtering, and extracting data.