Iterate LinkedHashMap in Java Example

This example shows how to iterate LinkedHashMap in Java. The example also shows various ways to iterate over LinkedHashMap keys, values and entries using an iterator and for loop.

How to iterate LinkedHashMap in Java?

There are various ways using which you can iterate over keys, values, and entries of the LinkedHashMap object in Java.

How to iterate over keys?

The entrySet method of the LinkedHashMap class returns a Set view of all the keys contained in the map. You can then iterate through keys as given below.

Using for loop

You can use the for loop to iterate through all the keys as given below.

LinkedHashMap<Integer, String> lhmap = new LinkedHashMap<Integer, String>();

lhmap.put(1, "One");

lhmap.put(2, "Two");

lhmap.put(3, "Three");

lhmap.put(4, "Four");

lhmap.put(5, "Five");

Set<Integer> keys = lhmap.keySet();

//using for loop

for(Integer key : keys){

System.out.println(key);

}

Using an Iterator

Alternatively, you can obtain an iterator object for the key set and iterate through the keys using the hasNext and the next methods of the Iterator.

//using an iterator

Iterator<Integer> iterator = keys.iterator();

while(iterator.hasNext()){

System.out.println(iterator.next());

}

Output

How to iterate over values?

The values method of the LinkedHashMap class returns a Collection view of all the values contained in the LinkedHashMap object. You can then iterate through them as given below.

Using for loop

LinkedHashMap<Integer, String> lhmap = new LinkedHashMap<Integer, String>();

lhmap.put(1, "One");

lhmap.put(2, "Two");

lhmap.put(3, "Three");

lhmap.put(4, "Four");

lhmap.put(5, "Five");

Collection<String> values = lhmap.values();

//using for loop

for(String value : values){

System.out.println(value);

}

Using an Iterator

You can also iterate through values using the hasNext and the next methods of the iterator as given below.

Collection<String> values = lhmap.values();

Iterator<String> iterator = values.iterator();

while(iterator.hasNext()){

System.out.println(iterator.next());

}

Output

One

Two

Three

Four

Five

How to iterate over entries (key-value mappings)?

The entrySet method of the LinkedHashMap class returns a Set view of all the entries (key-value mappings) contained in the LinkedHashMap object. You can then iterate through the mappings of the LinkedHashMap as given below.

Using for loop

LinkedHashMap<Integer, String> lhmap = new LinkedHashMap<Integer, String>();

lhmap.put(1, "One");

lhmap.put(2, "Two");

lhmap.put(3, "Three");

lhmap.put(4, "Four");

lhmap.put(5, "Five");

for( Map.Entry<Integer, String> entry : lhmap.entrySet() ){

System.out.println( entry.getKey() + "=>" + entry.getValue() );

}

Using an Iterator

You can also obtain an iterator for the entry set using the iterator method and then iterate using the hasNext and the next methods as given below.

Set<Map.Entry<Integer, String>> entries = lhmap.entrySet();

Iterator<Map.Entry<Integer, String>> iterator = entries.iterator();

Map.Entry<Integer, String> entry = null;

while(iterator.hasNext()){

entry = iterator.next();

System.out.println( entry.getKey() + "=>" + entry.getValue() );

}

Output

1=>One

2=>Two

3=>Three

4=>Four

5=>Five

This example is a part of the LinkedHashMap in Java Tutorial.

Please let me know your views in the comments section below.

References:
Java 8 LinkedHashMap

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Rahim

I have a master's degree in computer science and over 18 years of experience designing and developing Java applications. I have worked with many fortune 500 companies as an eCommerce Architect. Follow me on LinkedIn and Facebook.