Comparing between an Optional value with a normal variable doesn't work [duplicate]

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• How do I compare strings in Java? 23 answers

I tried to compare between these two variables but it always gave false

System.out.println(file_ext.get().toLowerCase() == "txt");
if (file_ext.get() == "txt") {
    System.out.println("Started");
} else {
    System.out.println("Incompatible file extension:" + file_ext.get());
}

but it prints this in the output:

false
Incompatible file extension:txt