[Java] Judgment of identity and equivalence

Judgment of Java identity and equivalence

I summarized about.

[What is the same / equivalent value]

Java has two meanings in the word "same"

--"** Same" that they are the same instance ** --The same value is "** equivalent" **

It's called.

[What is identity / equivalence]

-** Instances are different, but equivalence that they have the same value ** -** Identity that multiple variables refer to the same instance **

It's called.

Each judgment method is as follows.

-** Identity is == operator ** -** equals method ** to see if the referenced instances have the same value **

[Sample code]

The code below is like this.

1. Create one Sample instance with the main method
2. Prepare another Sample type variable and assign a reference to the first instance
3. Create an instance of Sample and assign a reference to that instance to sample1.

I wrote the detailed processing flow in the comment out, but in the end sample1 and sample2 will be different instances, so the result will be "false".

public class Sample {
    private int num;

    public Sample(int num) {
        this.setNum(num);
    }

    public int getNum() {
        return num;
    }

    public void setNum(int num) {
        this.num = num;
    }
}

public class Main {

    public static void main(String[] args) {

        // 1.Create one instance of Sample
        Sample sample1 = new Sample(10);

        // 2.Prepare another Sample type variable and assign a reference to the first instance
        Sample sample2 = sample1; // sample1,sample2 is "same" * Must be the same instance

        // 3.In addition, create an instance of Sample and assign a reference to that instance to sample1.
        sample1 = new Sample(10);//sample1 and sample2 are not "identical" because they have references to different instances

        System.out.println(sample1 == sample2); //Result false

    }

}

false

[Summary]

As a measure against Silver ...

-** Instances are different, but having the same value is called equivalence, and it is judged by the equals method. ** ** -** Identity is the property that multiple variables refer to the same instance, and is judged by the == operator. ** **

It's confusing, but remember that if you create a new instance with the same name, it will be a different instance.

References / Articles

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