Why does java's add report an error?

The Add method in Java reports an error due to type mismatch, specifically including: trying to add an object that does not match the expected type to the collection. Collections are immutable and elements cannot be added. The collection is full and no more elements can be added. Concurrent access exceptions may be caused by another thread modifying the collection. Null pointer exception if the collection is null. Format error, the key value format is incorrect. Security restrictions, some operations may be restricted.

Cause of error reported by Add method in Java

Type mismatch

• The most common cause of error is trying to add an object to the collection that does not match the expected type. For example, if the collection is a list of type Integer, you cannot add a value of type String.

Collections are immutable

• Some collection types (such as Collections.unmodifiableList) are immutable, which means that you cannot add or Delete elements. Attempting to add elements to an immutable collection results in an UnsupportedOperationException exception.

Collection is full

• For a limited-size collection (such as an array), if the collection is full, no more elements can be added. Attempting to add an element to a full collection results in an IndexOutOfBoundsException exception.

Concurrent Access Exception

• If multiple threads are being used and the collection is modified in another thread, a concurrent access exception may occur . For example, a ConcurrentModificationException exception occurs if another thread removes an element from the collection while an element is being added.

Other reasons

• Null Pointer Exception: If the collection is null, trying to add an element to it will cause a Null Pointer Exception.
• Format error: For some collection types (such as Map), the keys and values ​​must be in a specific format. If the format is incorrect, an IllegalArgumentException is thrown.
• Security restrictions: In a secure environment, certain operations may be restricted, such as adding elements to a collection. This may result in a SecurityException.

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