What does equals mean in java

The equals method compares the values ​​of Java objects for equality. Its working principles include: (1) reference comparison, to determine whether the objects are in the same memory location; (2) class comparison, to check whether the object types are the same; (3) field comparison, to compare field values ​​one by one. In order to correctly compare custom objects, the equals method should be overridden, following the guidelines of reflectivity, symmetry, transitivity, consistency, and null value handling. The equals method differs from the == operator in that it only compares object references, whereas the equals method compares object actual values.

The meaning of equals in Java

equals is used in Java to compare two Method to determine whether objects are equal. It is an instance method overridden from the Object class that is used to determine whether two objects have the same value.

How the equals method works

When the equals method is called, it performs the following steps:

1. Reference comparison: First, it checks whether the two objects are the same object (i.e., whether they refer to the same memory location). If yes, the objects are equal.
2. Class comparison: If two objects are not the same object, the equals method checks whether they are of the same class. If not, the objects are not equal.
3. Field comparison: If two objects are of the same class, the equals method will compare their fields. It compares field values ​​one by one and if all field values ​​are equal, the objects are equal.

Override the equals method

In order to enable custom objects to be compared correctly, you need to override the equals method. The following guidelines should be followed when overriding:

• Reflectivity: An object should always be equal to itself.
• Symmetry: If a.equals(b) is true, then b.equals(a) It should also be true.
• Transitiveness: If a.equals(b) is true, and b.equals(c) is true, then a.equals(c) should also be true.
• Consistency: As long as the values ​​of the two objects are equal, the equals method should return the same result each time it is called.
• Null value handling: If null values ​​are to be allowed, the equals method should handle null values ​​correctly.

The difference between equals and ==

== operator is used to compare whether the references of two objects are equal, while equals The method is used to compare whether the actual values ​​​​of two objects are equal. For primitive types (such as int or double), the == and equals operators behave the same. However, for object types (such as String or Date), == only compares object references, while the equals method compares the object's value .

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