Essential Books

optXXX vs getXXX methods

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JSONObject and JSONArray have a few methods that are very useful while dealing with a possibility that a value your are trying to get does not exist or is of another type. 

JSONObject obj = new JSONObject();
obj.putString("foo", "bar");

// For existing properties of the correct type, there is no difference
obj.getString("foo");        // returns "bar"
obj.optString("foo");        // returns "bar"
obj.optString("foo", "tux"); // returns "bar"

// However, if a value cannot be coerced to the required type, the behavior differs
obj.getInt("foo");      // throws JSONException
obj.optInt("foo");      // returns 0
obj.optInt("foo", 123); // returns 123

// Same if a property does not exist
obj.getString("undefined");        // throws JSONException
obj.optString("undefined");        // returns ""
obj.optString("undefined", "tux"); // returns "tux"

The same rules apply to the getXXX / optXXX methods of JSONArray.

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JSON in Java:
* JSON in Java
* Using Jackson Object Mapper
* JSON To Object Gson Library
* JSONObject.NULL
* JSON Builder - chaining methods
* Object To JSON Gson Library
* JSON Iteration
* optXXX vs getXXX methods
* Encoding data as JSON
* Decoding JSON data
* Extract single element from JSON
* JsonArray to Java List Gson Library
* Deserialize JSON collection to collection of Objects using Jackson
Table Of Contents
0 Inheritance
1 Getting started with Java
2 Streams
3 Exceptions
4 Collections
5 Lambda Expressions
6 Generics
7 File I/O
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11 Strings
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13 Default Methods
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15 Basic Control structures
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35 Nashorn JavaScript engine
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38 Iterator and Iterable
39 Operators
40 Asserting
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42 Properties Class
43 Preferences
44 Reflection API
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48 JSON in Java
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84 The Classpath
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90 XML XPath Evaluation
91 Performance Tuning
92 Parallel programming with ForkJoin framework
93 Common Pitfalls
94 Non-Access Modifiers
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118 Pitfalls - threads and concurrency
119 Splitting a string into fixed length parts
120 Pitfalls - nulls and NullPointerException
121 SecurityManager
122 JNDI
123 super keyword
124 java.util.Objects class
125 Java command: java and javaw
126 Atomic types
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128 Converting to and from strings
129 sun.misc.Unsafe
130 Java Memory Model
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137 Java Virtual Machine JVM
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142 Java SE 8 Features
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147 Using ThreadPoolExecutor in multi-threaded applications
148 Java Editions, versions, releases and distributions
149 Dynamic method dispatch
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152 Generating Java Code
153 JShell
154 Benchmarks
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156 Multi-release JAR files
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172 String Tokenizer
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176 Enum starting with a number
177 SortedMap
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180 StringBuffer
181 Choosing Collections
182 C++ Comparison
183 CompletableFuture
184 Contributors