I'm looking for a KeyValuePair class in Java.
Since java.util heavily uses interfaces there is no concrete implementation provided, only the Map.Entry interface.

Is there some canonical implementation I can import? It is one of those "plumbers programming" classes I hate to implement 100x times.

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10 Answers

The class AbstractMap.SimpleEntry is generic and can be useful.

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Android programmers could use BasicNameValuePair

Update:

BasicNameValuePair is now deprecated (API 22). Use Pair instead.

Example usage:

Pair<Integer, String> simplePair = new Pair<>(42, "Second");
Integer first = simplePair.first; // 42
String second = simplePair.second; // "Second"

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The Pair class from Commons Lang might help:

Pair<String, String> keyValue = new ImmutablePair("key", "value");

Of course, you would need to include commons-lang.

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Use of javafx.util.Pair is sufficient for most simple Key-Value pairings of any two types that can be instantiated.

Pair<Integer, String> myPair = new Pair<>(7, "Seven");
Integer key = myPair.getKey();
String value = myPair.getValue();

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import java.util.Map;
public class KeyValue<K, V> implements Map.Entry<K, V>
{ private K key; private V value; public KeyValue(K key, V value) { this.key = key; this.value = value; } public K getKey() { return this.key; } public V getValue() { return this.value; } public K setKey(K key) { return this.key = key; } public V setValue(V value) { return this.value = value; }
}

I like to use

Properties

Example:

Properties props = new Properties();
props.setProperty("displayName", "Jim Wilson"); // (key, value)
String name = props.getProperty("displayName"); // => Jim Wilson
String acctNum = props.getProperty("accountNumber"); // => null
String nextPosition = props.getProperty("position", "1"); // => 1

If you are familiar with a hash table you will be pretty familiar with this already

2

You can create your custom KeyValuePair class easily

public class Key<K, V>{ K key; V value; public Key() { } public Key(K key, V value) { this.key = key; this.value = value; } public void setValue(V value) { this.value = value; } public V getValue() { return value; } public void setKey(K key) { this.key = key; } public K getKey() { return key; }
}

My favorite is

HashMap<Type1, Type2>

All you have to do is specify the datatype for the key for Type1 and the datatype for the value for Type2. It's the most common key-value object I've seen in Java.

2

Hashtable<String, Object>

It is better than java.util.Properties which is by fact an extension of Hashtable<Object, Object>.

I've published a NameValuePair class in GlobalMentor's core library, available in Maven. This is an ongoing project with a long history, so please submit any request for changes or improvements.

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