21_Equals_and_HashCode.md

== Operator, equals(), hashCode

equals and hashCode are defined in the Object class, which is the parent object of all Java objects

-> Therefore, all Java objects inherit the equals and hashCode functions defined in the Object class

== Operator

• When the operands are primitive types (int, byte, short, long, float, double, boolean, char), it compares values,
• When the operands are other reference types, it compares the addresses they point to

equals()

public boolean equals(Object obj) {
    return (this == obj);
}

• Used to check whether 2 objects are identical
• It checks whether the 2 objects refer to the same thing
  • That is, 2 objects are identical only when they point to the same memory address
• When we create 2 identical strings, the 2 strings are allocated in different memory locations
  • However, the reason equals returns true is that the String class overrides the equals method to return true when the string contents are the same
    • It compares each character one by one and returns true if they are all identical
    • Therefore, even different objects are judged to be identical if they have the same string

hashCode()

public native int hashCode();

• It refers to a unique integer value that can identify an object
  • In the Object class, it is set to return the memory address of the object stored in heap memory
• The native keyword means the method is implemented using native code called JNI (Java Native Interface)
  • native is a keyword applicable only to methods, used when utilizing parts implemented in languages other than Java through JNI in Java
    • It is a keyword that enables using other languages from Java!
• hashCode is used to determine the location where data is stored when using data structures such as HashTable