EC
IllegalStateException
JavaERRORNotableState

Object in illegal state for this operation

Quick Answer

Check the object's state or lifecycle stage before calling the operation.

What this means

Thrown when a method is called at an inappropriate time — the object is not in the right state to perform the requested operation.

Why it happens
  1. 1Calling Iterator.remove() without a preceding next()
  2. 2Using a closed resource after close()

Fix

Check state before calling

Check state before calling
if (connection.isOpen()) {
    connection.send(data);
} else {
    connection.reconnect();
    connection.send(data);
}

Why this works

State check ensures the object is ready before the operation is attempted.

Code examples
Trigger with Iteratorjava
Iterator<String> it = list.iterator();
it.remove(); // IllegalStateException — no preceding next()
Correct Iterator removejava
while (it.hasNext()) {
    if (it.next().isEmpty()) it.remove(); // safe
}
Builder guardjava
if (!builder.isInitialized())
    throw new IllegalStateException("Call init() first");
Sources
Official documentation ↗

Java SE Documentation

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