Introduction
The Java LinkedHashMap class is Hash table and Linked list implementation of the Map interface, with predictable iteration order. Following are the important points about LinkedHashMap −
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The class provides all of the optional Map operations, and permits null elements.
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The Iteration over a HashMap is likely to be more expensive.
Class declaration
Following is the declaration for java.util.LinkedHashMap class −
public class LinkedHashMap<K,V> extends HashMap<K,V> implements Map<K,V>
Parameters
Following is the parameter for java.util.LinkedHashMap class −
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K − This is the type of keys maintained by this map.
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V − This is the the type of mapped values.
Class constructors
| Sr.No. | Constructor & Description |
|---|---|
| 1 |
LinkedHashMap() This constructs an empty insertion-ordered LinkedHashMap instance with the default initial capacity (16) and load factor (0.75). |
| 2 |
LinkedHashMap(int initialCapacity) This constructs an empty insertion-ordered LinkedHashMap instance with the specified initial capacity and a default load factor (0.75). |
| 3 |
LinkedHashMap(int initialCapacity, float loadFactor) This constructs an empty insertion-ordered LinkedHashMap instance with the specified initial capacity and load factor. |
| 4 |
LinkedHashMap(int initialCapacity, float loadFactor, boolean accessOrder) This constructs an empty LinkedHashMap instance with the specified initial capacity, load factor and ordering mode. |
| 5 |
LinkedHashMap(Map<? extends K,? extends V> m) This constructs an insertion-ordered LinkedHashMap instance with the same mappings as the specified map. |
Class methods
| Sr.No. | Method & Description |
|---|---|
| 1 |
This method returns true if this map maps one or more keys to the specified value. |
| 2 |
This method returns a Set view of the mappings contained in this map. |
| 3 |
This method returns the value to which the specified key is mapped, or null if this map contains no mapping for the key. |
| 4 |
This method returns a Set view of the keys contained in this map. |
| 5 |
This method returns a Collection view of the values contained in this map. |
Methods inherited
This class inherits methods from the following classes −
- java.util.HashMap
- java.util.AbstarctMap
- java.util.Object
- java.util.Map
Getting a Value from LinkedHashMap Example
The following example shows the usage of Java LinkedHashMap get() method to get a value based on a key from a Map. We”ve created a Map object of Integer,Integer. Then few entries are added, map is printed. Using get() method, a value is retrieved and printed.
package com.tutorialspoint;
import java.util.LinkedHashMap;
public class LinkedHashMapDemo {
public static void main(String args[]) {
// create hash map
LinkedHashMap<Integer,Integer> newmap = new LinkedHashMap<>();
// populate hash map
newmap.put(1, 1);
newmap.put(2, 2);
newmap.put(3, 3);
System.out.println("Initial map elements: " + newmap);
System.out.println("Value: " + newmap.get(1));
}
}
Output
Let us compile and run the above program, this will produce the following result.
Initial map elements: {1=1, 2=2, 3=3}
Value: 1