How to change value in HashMap Java?

How to change value in HashMap Java?

In Java, a HashMap is a collection that stores key-value pairs. If you want to change the value associated with a specific key in a HashMap, you can simply use the put() method to replace the old value with the new value. Here is how you can change the value in a HashMap:

“`java
HashMap map = new HashMap<>();
map.put(“key”, “oldValue”); // Adding a key-value pair
System.out.println(“Old value: ” + map.get(“key”)); // Getting the old value
map.put(“key”, “newValue”); // Changing the value
System.out.println(“New value: ” + map.get(“key”)); // Getting the new value
“`

By using the put() method with the same key as before, you can update the value associated with that key in the HashMap.

FAQs

1. How to add a key-value pair to a HashMap in Java?

To add a key-value pair to a HashMap in Java, you can use the put() method like this:
“`java
map.put(“key”, “value”);
“`

2. How to check if a key exists in a HashMap?

You can use the containsKey() method to check if a key exists in a HashMap:
“`java
if(map.containsKey(“key”)) {
System.out.println(“Key exists”);
} else {
System.out.println(“Key does not exist”);
}
“`

3. How to get all keys from a HashMap in Java?

To get all keys from a HashMap in Java, you can use the keySet() method like this:
“`java
Set keys = map.keySet();
“`

4. How to get all values from a HashMap in Java?

To get all values from a HashMap in Java, you can use the values() method like this:
“`java
Collection values = map.values();
“`

5. How to remove a key-value pair from a HashMap?

You can use the remove() method to remove a key-value pair from a HashMap like this:
“`java
map.remove(“key”);
“`

6. How to get the size of a HashMap in Java?

You can use the size() method to get the size of a HashMap in Java like this:
“`java
int size = map.size();
“`

7. How to check if a value exists in a HashMap?

You can use the containsValue() method to check if a value exists in a HashMap like this:
“`java
if(map.containsValue(“value”)) {
System.out.println(“Value exists”);
} else {
System.out.println(“Value does not exist”);
}
“`

8. How to iterate over a HashMap in Java?

You can use a for-each loop to iterate over a HashMap in Java like this:
“`java
for(Map.Entry entry : map.entrySet()) {
System.out.println(“Key: ” + entry.getKey() + “, Value: ” + entry.getValue());
}
“`

9. How to clear a HashMap in Java?

You can use the clear() method to clear a HashMap in Java like this:
“`java
map.clear();
“`

10. How to get a value based on a key from a HashMap in Java?

You can use the get() method to get a value based on a key from a HashMap in Java like this:
“`java
String value = map.get(“key”);
“`

11. How to check if a HashMap is empty in Java?

You can use the isEmpty() method to check if a HashMap is empty in Java like this:
“`java
if(map.isEmpty()) {
System.out.println(“HashMap is empty”);
} else {
System.out.println(“HashMap is not empty”);
}
“`

12. How to replace a value in a HashMap if it exists, otherwise add a new key-value pair?

You can use the putIfAbsent() method to replace a value in a HashMap if it exists, otherwise add a new key-value pair like this:
“`java
map.putIfAbsent(“key”, “newValue”);
“`

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