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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:
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What does %10d do?
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What does the term 'immutable' mean in the context of Java Strings?
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Name 10 methods of the String class.
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Which of the following are objectives in Chapter 3? (Select all that apply)
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What does the new operator accomplish?
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What is a null reference?
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What is an alias?
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Write a declaration for a String variable called author and initialize it to 'Fred Brooks'.
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Write a statement that prints the value of a String object called title in all uppercase letters.
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What is a Java package?
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What does the java.net package contain?
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What does an import declaration accomplish?
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Why doesn't the String class have to be specifically imported into our programs?
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What do the calls rand.nextInt() and rand.nextInt(20) return when rand is a Random object?
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What is a class method?
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What are the steps to output a floating point value as a percentage in Java?
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How can we represent a primitive value as an object?
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What does garbage collection refer to?
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What is the purpose of the Scanner class?
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What is 'Half Even Rounding'?
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Write a program to format the amount 1150.45 to the correct currency format using the NumberFormat class.
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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 fromjava.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()
orMath.pow()
.
Formatting Output
- The
NumberFormat
andDecimalFormat
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()
, andnextDouble()
fetch input tokens asynchronously. - Creating a
Scanner
object for keyboard input is done withScanner 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 thejava.awt
package are essential for drawing operations. - The use of APIs like
java.text
andjava.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 injava.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.