Jason Cameron

The gritty details

2 min read

1. Definitions:

  • Accessor method: A “getter” that returns the value of a private variable.
  • Actual parameter: The value you pass when calling a method.
  • Explicit parameter: The parameter declared in the method’s definition.
  • Formal parameter: Another term for the parameter declared in the method.
  • Implicit parameter: The hidden reference to the current object (via instance variables).
  • Mutator method: A “setter” that changes a private variable’s value.
  • Null reference: Indicates no object is referenced.
  • Pass by reference: The reference (address) is passed; changes to arrays affect the original.
  • Pass by value: A copy is passed; changes inside the method don’t affect the original.
  • Promoting: Converting a smaller data type to a larger one automatically.
  • Scope: The area of code where a variable is accessible.
  • String literal: A fixed sequence of characters like “Hello”.

2. Variable Scope and Initialization:

  • Local variables must be explicitly initialized before use.
  • Instance variables are automatically given default values.
  • Local variables vanish after the method finishes.

3. What’s Happening in RAM:

  • String m = “My name”; A String with “My name” is created; m points to it.
  • String r = “Your name”; Similarly, a String for “Your name” is created; r points to it.
  • r = m; Now, r points to the same object as m.
  • m = null; m no longer points to the object; r still does.

4. compareTo(), compareToIgnoreCase(), and equals():

  • compareTo(): Compares strings by Unicode values; case-sensitive.
  • compareToIgnoreCase(): Like compareTo but ignores case.
  • equals(): Checks if two strings have the same content.

5. The Object Class:

  • equals(): Tests if two objects are logically equal (by default, checks references).
  • hashCode(): Returns an integer for an object, used in hash-based collections.
  • toString(): Provides a String representation of an object.

6. Class Downcasting:

  • Converting a superclass reference to a subclass reference.
  • Caution: Only do this if the object is actually an instance of the subclass; otherwise, you get a ClassCastException.

7. Class Casting:

  • Refers mainly to downcasting and converting between class types.
  • Essentially, it’s about converting references from one type to another.

8. PDT Casting:

  • Converting between primitive data types.
  • Caution: Downcasting (larger to smaller types) can lose data; booleans can’t be cast.

9. Static vs. Instance Methods:

  • Static/class methods: Belong to the class and can be called without an instance.
  • Instance/member methods: Require an object because they operate on instance data.

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