CODEWITHSUNDEEP
javadictionaryin-place
jrharshath
jrharshath

Reputation: 26583

Updating a java map entry

I'm facing a problem that seems to have no straighforward solution.

I'm using java.util.Map, and I want to update the value in a Key-Value pair.

Right now, I'm doing it lik this:

private Map<String,int> table = new HashMap<String,int>();
public void update(String key, int val) {
    if( !table.containsKey(key) ) return;
    Entry<String,int> entry;
    for( entry : table.entrySet() ) {
        if( entry.getKey().equals(key) ) {
            entry.setValue(val);
            break;
        }
    }
}

So is there any method so that I can get the required Entry object without having to iterate through the entire Map? Or is there some way to update the entry's value in place? Some method in Map like setValue(String key, int val)?

jrh

Upvotes: 78

Views: 151875

Answers (3)

skaffman
skaffman

Reputation: 403491

Use

table.put(key, val);

to add a new key/value pair or overwrite an existing key's value.

From the Javadocs:

V put(K key, V value): Associates the specified value with the specified key in this map (optional operation). If the map previously contained a mapping for the key, the old value is replaced by the specified value. (A map m is said to contain a mapping for a key k if and only if m.containsKey(k) would return true.)

Upvotes: 167

Priyank
Priyank

Reputation: 14387

If key is present table.put(key, val) will just overwrite the value else it'll create a new entry. Poof! and you are done. :)

you can get the value from a map by using key is table.get(key); That's about it

Upvotes: 14

mkoeller
mkoeller

Reputation: 4477

You just use the method

public Object put(Object key, Object value)

if the key was already present in the Map then the previous value is returned.

Upvotes: 6

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