30_How_To_Compare_java_Objects

How to Compare Java Objects - equals() & Hashcode() !

class Student {
    private String name;

    public Student(String name) {
        this.name = name;
    }
}

public class MainApp {
    public static void main(String[] args) {
        Student s1 = new Student("Anu");
        Student s2 = new Student("Ann");
        Student s3 = new Student("Ann");


        // Comparing two objects using  .equals()

        System.out.println(s1.equals(s2));     // false - content not same
        System.out.println(s2.equals(s3));    // true - content same // value of instance variable same

    }
}

equals()

equals() is a method used to compare two objects in java.

2 objects are said to be equal -

       > When they belong to the same class type.

       > values of instance variables should be same

       > 2 objects are going to have same hashcode

  NOTE: When 2 objects are equal >> they will have same hashcode value!

Internal representation of .equal()

@Override
    public boolean equals(Object obj) { // comparing 2 objects// parameter is of parent class// datatype of reference is obj
        // Step 1: Check if both references point to the same object

        if (this == obj) { // this talks about the current instance// comparing s1.equals(s1)
            return true; // then return true!
        }

        // Step 2: Check if the passed object is null 
        if (obj == null )// passing null - couldn't compare which doesn't exist ie obj reference is NULL
          return false; //   return false!

        // step 3: ocheck if the passed obj is of the same class
        if(getClass() != obj.getClass()) { // getClass() gives the class type // if 2 classes are not equal - return false
            return false; // return false
        }


        // Then do type casting - after that value of each instance variable of one object is compared with other one.

Where do we use .equals() in Automation Framework?

 .equals() is commonly used in assertions to compare expected and actual results

Student expectedData = new Student("Ann", 20, 18, 75, 82, 69, "B");

System.out.println(expectedData);

Student actualData = new Student("Ann", 20, 18, 75, 82, 69, "B");

System.out.println(expectedData.equals(actualData));  // true → if equals() is properly overridden