Java Language
- Getting started with Java Language
- Top 10 Java Errors with Solutions
- Awesome Book
- Awesome Community
- Awesome Course
- Awesome Tutorial
- Awesome YouTube
- 2D Graphics in Java
- Alternative Collections
- Annotations
- Apache Commons Lang
- AppDynamics and TIBCO BusinessWorks Instrumentation for Easy Integration
- Applets
- Arrays
- Asserting
- Atomic Types
- Audio
- Autoboxing
- Basic Control Structures
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- Calendar and its Subclasses
- Character encoding
- Choosing Collections
- Class - Java Reflection
- Classes and Objects
- Classloaders
- Collection Factory Methods
- Collections
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- Common Java Pitfalls
- Comparable and Comparator
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- Concurrent Collections
- Concurrent Programming (Threads)
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- Converting to and from Strings
- Creating Images Programmatically
- Currency and Money
- Date Class
- Dates and Time (java.time.*)
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- Documenting Java Code
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- Enum starting with number
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- Exceptions and exception handling
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- Installing Java (Standard Edition)
- Interfaces
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- Java Pitfalls - Exception usage
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- Java Pitfalls - Nulls and NullPointerException
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- Localization and Internationalization
- LocalTime
- log4j / log4j2
- Logging (java.util.logging)
- Maps
- Add an element
- Add multiple items
- Check if key exists
- Clear the map
- Creating and Initializing Maps
- Iterating Map Entries Efficiently
- Iterating through the contents of a Map
- Merging, combine and composing Maps
- Usage of HashMap
- Use custom object as key
- Using Default Methods of Map from Java 8
- Modules
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- Nashorn JavaScript engine
- Nested and Inner Classes
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- sun.misc.Unsafe
- super keyword
- The Classpath
- The Java Command - 'java' and 'javaw'
- The java.util.Objects Class
- ThreadLocal
- TreeMap and TreeSet
- Type Conversion
- Unit Testing
- Using Other Scripting Languages in Java
- Using the static keyword
- Using ThreadPoolExecutor in MultiThreaded applications.
- Varargs (Variable Argument)
- Visibility (controlling access to members of a class)
- WeakHashMap
- XJC
- XML Parsing using the JAXP APIs
- XML XPath Evaluation
- XOM - XML Object Model
Java Language Maps
Introduction
The java.util.Map interface represents a mapping between keys and their values. A map cannot contain duplicate keys; and each key can map to at most one value.
Since Map is an interface, then you need to instantiate a concrete implementation of that interface in order to use it; there are several Map implementations, and mostly used are the java.util.HashMap and java.util.TreeMap
Remarks
A map is an object which store keys with an associated value for each key. A key and its value are sometimes called a key/value pair or an entry. Maps typically provide these features:
- Data is stored into the map in key/value pairs.
- The map may contain only one entry for a particular key. If a map contains an entry with a particular key, and you try to store a second entry with the same key, then the second entry will replace the first. In other words, this will change the value associated with the key.
- Maps provide fast operations to test whether a key exists in the map, to fetch the value associated with a key, and to remove a key/value pair.
The most commonly used map implementation is HashMap. It works well with keys that are strings or numbers.
Plain maps such as HashMap are unordered. Iterating through key/value pairs may return individual entries in any order. If you need to iterate through map entries in a controlled fashion, you should look at the following:
-
Sorted maps such as TreeMap will iterate through keys in their natural order (or in an order that you can specify, by providing a Comparator). For example, a sorted map using numbers as keys would be expected to iterate through its entries in numeric order.
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LinkedHashMap permits iterating through entries in the same order that they were inserted into the map, or by the order of most recently accessed.
Maps Related Examples
- Add an element
- Add multiple items
- Check if key exists
- Clear the map
- Creating and Initializing Maps
- Iterating Map Entries Efficiently
- Iterating through the contents of a Map
- Merging, combine and composing Maps
- Usage of HashMap
- Use custom object as key
- Using Default Methods of Map from Java 8
