Effective Java (2nd ed.) [Bloch 2008-05-28].pdf

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Effective Java
™
Second Edition
Joshua Bloch
Upper Saddle River, NJ • Boston • Indianapolis • San Francisco
New York • Toronto • Montreal London • Munich • Paris • Madrid
Capetown • Sydney • Tokyo • Singapore • Mexico City
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ISBN-13: 978-0-321-35668-0
ISBN-10:
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Text printed in the United States on recycled paper at Courier in Stoughton, Massachusetts.
First printing, May 2008
Contents
Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xv
Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
2 Creating and Destroying Objects. . . . . . . . . . . . . . . . . . .5
Item 1: Consider static factory methods instead of constructors . . . 5
Item 2: Consider a builder when faced with many constructor
parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Item 3: Enforce the singleton property with a private
constructor or an enum type . . . . . . . . . . . . . . . . . . . . . . . 17
Item 4: Enforce noninstantiability with a private constructor . . . . 19
Item 5: Avoid creating unnecessary objects . . . . . . . . . . . . . . . . . 20
Item 6: Eliminate obsolete object references . . . . . . . . . . . . . . . . . 24
Item 7: Avoid finalizers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3 Methods Common to All Objects. . . . . . . . . . . . . . . . . .33
Item 8: Obey the general contract when overriding
equals
. . . . .
Item 9: Always override
hashCode
when you
override
equals
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Item 10: Always override
toString
. . . . . . . . . . . . . . . . . . . . . . . .
Item 11: Override
clone
judiciously . . . . . . . . . . . . . . . . . . . . . . . .
Item 12: Consider implementing
Comparable
. . . . . . . . . . . . . . . .
33
45
51
54
62
ix
x
CONTENTS
4 Classes and Interfaces. . . . . . . . . . . . . . . . . . . . . . . . . . . 67
Item 13: Minimize the accessibility of classes and members . . . . . . 67
Item 14: In public classes, use accessor methods,
not public fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Item 15: Minimize mutability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Item 16: Favor composition over inheritance . . . . . . . . . . . . . . . . . . 81
Item 17: Design and document for inheritance or else prohibit it . . 87
Item 18: Prefer interfaces to abstract classes . . . . . . . . . . . . . . . . . . 93
Item 19: Use interfaces only to define types. . . . . . . . . . . . . . . . . . . 98
Item 20: Prefer class hierarchies to tagged classes . . . . . . . . . . . . . 100
Item 21: Use function objects to represent strategies . . . . . . . . . . . 103
Item 22: Favor static member classes over nonstatic . . . . . . . . . . . 106
5 Generics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
Item 23: Don’t use raw types in new code . . . . . . . . . . . . . . . . . . . 109
Item 24: Eliminate unchecked warnings. . . . . . . . . . . . . . . . . . . . . 116
Item 25: Prefer lists to arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119
Item 26: Favor generic types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
Item 27: Favor generic methods . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
Item 28: Use bounded wildcards to increase API flexibility . . . . . 134
Item 29: Consider typesafe heterogeneous containers . . . . . . . . . . 142
6 Enums and Annotations . . . . . . . . . . . . . . . . . . . . . . . . 147
Item 30: Use enums instead of
int
constants. . . . . . . . . . . . . . . . . 147
Item 31: Use instance fields instead of ordinals . . . . . . . . . . . . . . . 158
Item 32: Use
EnumSet
instead of bit fields . . . . . . . . . . . . . . . . . . . 159
Item 33: Use
EnumMap
instead of ordinal indexing. . . . . . . . . . . . . 161
Item 34: Emulate extensible enums with interfaces . . . . . . . . . . . . 165
Item 35: Prefer annotations to naming patterns . . . . . . . . . . . . . . . 169
Item 36: Consistently use the
Override
annotation. . . . . . . . . . . . 176
Item 37: Use marker interfaces to define types . . . . . . . . . . . . . . . 179
7 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 181
Item 38: Check parameters for validity . . . . . . . . . . . . . . . . . . . . . 181
Item 39: Make defensive copies when needed . . . . . . . . . . . . . . . . 184
Item 40: Design method signatures carefully . . . . . . . . . . . . . . . . . 189
Item 41: Use overloading judiciously . . . . . . . . . . . . . . . . . . . . . . . 191
CONTENTS
xi
Item 42: Use varargs judiciously . . . . . . . . . . . . . . . . . . . . . . . . . . 197
Item 43: Return empty arrays or collections, not nulls . . . . . . . . . 201
Item 44: Write doc comments for all exposed API elements . . . . 203
8 General Programming . . . . . . . . . . . . . . . . . . . . . . . . .209
Item 45: Minimize the scope of local variables . . . . . . . . . . . . . . .
Item 46: Prefer for-each loops to traditional
for
loops . . . . . . . . .
Item 47: Know and use the libraries . . . . . . . . . . . . . . . . . . . . . . .
Item 48: Avoid
float
and
double
if exact answers
are required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Item 49: Prefer primitive types to boxed primitives . . . . . . . . . . .
Item 50: Avoid strings where other types are more appropriate . .
Item 51: Beware the performance of string concatenation . . . . . .
Item 52: Refer to objects by their interfaces . . . . . . . . . . . . . . . . .
Item 53: Prefer interfaces to reflection . . . . . . . . . . . . . . . . . . . . .
Item 54: Use native methods judiciously. . . . . . . . . . . . . . . . . . . .
Item 55: Optimize judiciously . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Item 56: Adhere to generally accepted naming conventions . . . . .
209
212
215
218
221
224
227
228
230
233
234
237
9 Exceptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .241
Item 57: Use exceptions only for exceptional conditions . . . . . . .
Item 58: Use checked exceptions for recoverable conditions
and runtime exceptions for programming errors . . . . . . .
Item 59: Avoid unnecessary use of checked exceptions . . . . . . . .
Item 60: Favor the use of standard exceptions. . . . . . . . . . . . . . . .
Item 61: Throw exceptions appropriate to the abstraction. . . . . . .
Item 62: Document all exceptions thrown by each method. . . . . .
Item 63: Include failure-capture information in
detail messages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Item 64: Strive for failure atomicity . . . . . . . . . . . . . . . . . . . . . . .
Item 65: Don’t ignore exceptions . . . . . . . . . . . . . . . . . . . . . . . . .
241
244
246
248
250
252
254
256
258
10 Concurrency. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .259
Item 66: Synchronize access to shared mutable data. . . . . . . . . . .
Item 67: Avoid excessive synchronization . . . . . . . . . . . . . . . . . .
Item 68: Prefer executors and tasks to threads. . . . . . . . . . . . . . . .
Item 69: Prefer concurrency utilities to
wait
and
notify
. . . . . . .
259
265
271
273

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