Java Foundations Chapter 3 Quiz

Java Object-Oriented Concepts

• Chapter 3 covers object creation, referencing, and Java's classes and methods.
• Objects are instantiated using the new operator, invoking the class constructor.
• A null reference indicates no object is associated; checked using the reserved word null.
• Aliasing occurs when multiple references point to the same object, affecting garbage collection.

String Manipulation

• Strings can be declared and initialized in Java using String author = "Fred Brooks";.
• Conversion methods like toUpperCase() enable string manipulation.
• Substring methods extract parts of strings, e.g., String front = description.substring(0, 10);.

Java Packages

• Packages group related classes, e.g., java.util for utility classes, java.lang for fundamental classes.
• Importing classes or entire packages allows easier access to their features.
• The Scanner class from java.util facilitates user input handling.

Randomness and Math

• The Random class generates pseudorandom numbers, crucial for simulations and testing.
• Methods like rand.nextInt(20) return random integers within specified ranges.
• The Math class offers static methods for complex calculations, e.g., Math.sin() or Math.pow().

Formatting Output

• The NumberFormat and DecimalFormat classes help format output for currency and percentages.
• Example to format currency:

  NumberFormat currFmt = NumberFormat.getCurrencyInstance();
  

• Patterns in DecimalFormat allow control over decimal precision (e.g., 0.### for three decimal places).

Object States and Behaviors

• Objects encapsulate state (attributes) and behaviors (methods), facilitating OOP principles.
• Encapsulation helps list attributes like characters and length for String class.
• Constructor methods initialize object states at creation, ensuring readiness for use.

Enumerated Types and Autoboxing

• Enumerated types define limited, type-safe sets like movie ratings using enum Ratings {G, PG, PG13, R, NC17}.
• Wrapper classes convert primitive values to objects, with autoboxing automating this process.

Memory Management

• Java uses stack and heap for memory management, distinguishing where variables and objects are stored.
• Objects can only be garbage collected when no valid references remain, freeing up memory.

Input Handling

• The Scanner class reads various input types, relying on whitespace to delineate tokens.
• Methods like next(), nextInt(), and nextDouble() fetch input tokens asynchronously.
• Creating a Scanner object for keyboard input is done with Scanner scan = new Scanner(System.in);.

Rounding and Formatting Patterns

• Java supports various formatting patterns in printf, e.g., %f for floating-point and %d for integers.
• Half even rounding helps in achieving statistical fairness when rounding values.
• Common formatting patterns are provided by DecimalFormat and can include scientific notation, etc.

Integrating Classes

• Classes like Graphics from the java.awt package are essential for drawing operations.
• The use of APIs like java.text and java.util enriches Java programming with powerful formatting and utility functions.

General Java Class Library

• The Java standard library is organized into packages, ensuring modularity and reusability of classes.
• Each package serves a unique purpose, from GUI frameworks in java.awt to networking in java.net.

String Class Functionality

• String objects are immutable; once created, their state cannot change.
• Common methods include length(), charAt(), replace(), and many others that operate on string data.

This study guide summarizes key points from Java Chapter 3, focusing on essential concepts involving classes, objects, and their manipulation.