Using Classes and Objects - Java Software Solutions: Foundations of Program Design - page 155

Summary of Key Concepts

The new operator returns a reference to a newly created object. ■

Multiple reference variables can refer to the same object.

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Usually a method is executed on a particular object, which affects the results. ■

A class library provides useful support when developing programs.

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The Java standard class library is organized into packages.

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All classes of the java.lang package are automatically imported for every
program.

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A pseudorandom number generator performs a complex calculation to
create the illusion of randomness.

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All methods of the Math class are static, meaning they are invoked through
the class name.

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The printf method was added to Java to support the migration of legacy
systems.

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Enumerated types are type-safe, ensuring that invalid values will not be used.

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A wrapper class allows a primitive value to be managed as an object. ■

Autoboxing provides automatic conversions between primitive values and
corresponding wrapper objects.

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Containers are special GUI components that hold and organize other
components.

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A frame is displayed as a separate window, but a panel can be displayed
only as part of another container.

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Every container is managed by a layout manager.

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Panels can be nested to create an intricate containment hierarchy of com-
ponents.

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A label can contain text, an image, or both.

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Exercises
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online and get instant feedback.
EX 3.1

Write a statement that prints the number of characters in a
String object called overview .

EX 3.2 Write a statement that prints the 8th character of a String

object called introduction .