What is the difference between equals and == in Java?

In Java, both equals() and == are used to compare the equality of two objects, but there are some important differences between them.

1. How to use it: The equals() method needs to be called by an object, whereas == can be used directly as an operator.
2. Comparison of object types: the `equals()` method can be used to compare two different types of objects, it first checks if the types of the two objects are the same, then compares their contents. The `==` operator can only be used to compare whether two objects’ references are the same, i.e., whether they point to the same memory address.
3. Default implementation: In Java, all classes inherit from the Object class, which provides a default implementation of the equals() method for comparing object references. To compare the contents of objects for equality, the equals() method needs to be overridden in the specific class.
4. Rewrite the equals() method: When comparing the contents of two objects, it is necessary to override the equals() method in the class and define the comparison rules based on actual requirements. Typically, this involves comparing whether certain attributes or states of the objects are equal.
5. Compare String objects: For the String class, the equals() method has been overridden to compare the content of the strings to check if they are equal. Therefore, when comparing two string objects, one should use the equals() method.

In conclusion, the equals() method is used to compare if the contents of two objects are equal, while the == operator is used to compare if the references of two objects are the same. When comparing objects, choose the appropriate method based on specific needs.