Java Foundations Chapter 3 Quiz

Questions and Answers

What does the method `setRoundingMode()` do?

It sets the rounding mode for formatting.

What formats does DecimalFormat commonly use?

0 digit(int, short, byte), # digit, zero shows as absent, decimal operator, , grouping separator, E scientific notation.

What do %f and %d do in a printf() method?

%f means floating point, %d means decimal.

Match the following conversion specifiers with their meanings:

%d = Decimal %ld = Long %f = Floating point %e = Floating point in scientific notation %s = String %b = Boolean Signup and view all the answers

What does %10d do?

Uses a field 10 wide. Signup and view all the answers

What does the term 'immutable' mean in the context of Java Strings?

In Java, Strings are immutable, meaning their value cannot be changed once created. Signup and view all the answers

Name 10 methods of the String class.

Various String methods include: length(), trim(), charAt(), substring(), indexOf(), replace(), toLowerCase(), toUpperCase(), split(), and equals(). Signup and view all the answers

Which of the following are objectives in Chapter 3? (Select all that apply)

Discuss the creation of objects and the use of object reference variables. Signup and view all the answers

What does the new operator accomplish?

The new operator creates a new instance (an object) of the specified class. Signup and view all the answers

What is a null reference?

A null reference is a reference that does not refer to any object. Signup and view all the answers

What is an alias?

Two references are aliases of each other if they refer to the same object. Signup and view all the answers

Write a declaration for a String variable called author and initialize it to 'Fred Brooks'.

String author = new String('Fred Brooks'); Signup and view all the answers

Write a statement that prints the value of a String object called title in all uppercase letters.

System.out.println(title.toUpperCase()); Signup and view all the answers

What is a Java package?

A Java package is a collection of related classes. Signup and view all the answers

What does the java.net package contain?

The java.net package contains classes that support network communication. Signup and view all the answers

What does an import declaration accomplish?

An import declaration establishes the fact that a program uses a particular class. Signup and view all the answers

Why doesn't the String class have to be specifically imported into our programs?

Because the String class is part of the java.lang package, which is automatically imported into any Java program. Signup and view all the answers

What do the calls rand.nextInt() and rand.nextInt(20) return when rand is a Random object?

rand.nextInt() returns a random integer in the range of all possible int values, while rand.nextInt(20) returns a random number in the range 0 to 19. Signup and view all the answers

What is a class method?

A class method can be invoked through the name of the class that contains it, such as Math.abs. Signup and view all the answers

What are the steps to output a floating point value as a percentage in Java?

Obtain a NumberFormat object using NumberFormat.getPercentInstance() and pass the value to the format method. Signup and view all the answers

How can we represent a primitive value as an object?

A wrapper class is defined for each primitive type. Signup and view all the answers

What does garbage collection refer to?

Garbage collection is the process of reclaiming memory space that can no longer be used by a program. Signup and view all the answers

What is the purpose of the Scanner class?

The Scanner class is used for reading input values from various sources, including the keyboard. Signup and view all the answers

What is 'Half Even Rounding'?

It rounds towards the nearest whole number unless the neighbours are equidistant, in which case it rounds towards the even neighbour. Signup and view all the answers

Write a program to format the amount 1150.45 to the correct currency format using the NumberFormat class.

import java.text.NumberFormat; NumberFormat currFmt = NumberFormat.getCurrencyInstance(); double amount = 1150.45; System.out.println('Amount: ' + currFmt.format(amount)); Signup and view all the answers

Study Notes

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.

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Description

Test your understanding of Chapter 3 from Java Foundations, focusing on the creation and use of classes and objects. This quiz covers essential concepts like object reference variables, string services, and output formatting. Perfect for reinforcing your knowledge of the Java standard class library.