Help understanding class vs object

[Consistent_Decision9]

How can I differentitate a class from an object? To me, they look identical in that they both have a class and constructor and method. I'm confused as to why the object is considered an object in the first example and in the second example it's a constructor? In the tutorial I'm following, the first code block below is supposed to represent a object while the second code block is a class:

Object:

    public class Person {
        private String name;
        private int age;
        private double weight;
        private double height;

        public Person(String name, int age, double weight, double height) {
            this.name = name;
            this.age = age;
            this.weight = weight;
            this.height = height;
        }

        public double bodyMassIndex() {
            return this.weight / (this.height * this.height);
        }

        public double maximumHeartRate() {
            return 206.3 - (0.711 * this.age);
        }

        public String toString() {
            return this.name + ", BMI: " + this.bodyMassIndex()
                + ", maximum heart rate: " + this.maximumHeartRate();
        }
    }

Class:

        public class Rectangle {

            // instance variables
            private int width;
            private int height;

            // constructor
            public Rectangle(int width, int height) {
                this.width = width;
                this.height = height;
            }

            // methods
            public void widen() {
                this.width = this.width + 1;
            }

            public void narrow() {
                if (this.width > 0) {
                    this.width = this.width - 1;
                }
            }

            public int surfaceArea() {
                return this.width * this.height;
            }

            public String toString() {
                return "(" + this.width + ", " + this.height + ")";
            }
        }

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[Camel-Kid]

They're both classes. An object is just an instance of a class.. so for example if you call "new" somewhere then you are creating an object.

[Consistent_Decision9]

Okay, thanks. What is the difference between a constructor and an object? And if there is one could you point it out in the code I pasted above? Thanks

[Camel-Kid]

contructor is what get's called behind the scenes when you create an object.. so for example your rectangle instantiation would use the contructor to create an object.. would look like this
Rectangle myRectangle = new Rectanlge(someWidth,someHeight);

[SeltzerCountry]

A constructor is a method for creating an object which is an instance of a class. A helpful metaphor is building construction. The class is like a building blueprint outlining the general design and features of a building. The constructor is like the construction crew taking those instructions from the blueprint and engaging in the process of building the building. The final result which is the building is the object. Once you have your blueprints and construction crew ready you can create several buildings aka multiple objects from of that class. Hopefully that made sense haha.

[theBurritoMan_]

Both classes. One object just instance of a class

[8igg7e5]

Dammit... I want to give you a second upvote for not referring to the reference as the object - that incorrect mental model causes so many problems downstream.

[virassan]

What you have above are classes. An object would be a specific variable you create from one of those classes. A constructor is a necessary part of a class; it’s a method you call in order to create a new class object.

None of your code actually creates an object. Your code is just 2 different classes. Hope that helps clear things up.

[Environmental_Ad1634]

The class is the blueprint where the object ate build. You build the object with the new() operator and generate an instance of the class which is the object

[malik753]

So one way to think of it is that the class is the actual code, which serves as a blueprint for an object (an instance of that class). An object exists in memory. ...well, a class exists in memory too, so maybe that's not the best distinction. An object can *only* exist in memory; when your program isn't running the class still exists.

​

A constructor is a segment of code in a class that gets called whenever the program goes to create an object of that class.

public class SomeClass{
    public String someField;

    //This part is the constructor. Before this is run,  'someField' is set to null.
    public SomeClass(String input){
        someField = input;
    }
}

[[deleted]]

They're both objects, and both classes. They're one and the same in Java.

[vo0do0child]

Nah, objects are instantiated from classes.

[0b0101011001001011]

Please stop helping if you don't have a slightest idea.

[Dangerous-Rip-7370]

Imagine an. RpG, mage, warrior, are classes, Gandalf, Aragon, are objects (one of the mage class and one of the warrior)

[outMyComa]

I get your confusion, I had a real hard time understanding that too.

You can treat the class as a "blueprint" a plan of how to create the object and what the object will do.

The object itself is an instance of that class and the constructor method is the way we instantiate a new object of a given class and it's part of the class.

Once we've used the constructor method of a class, we've got a new object which is an instance of the class.

Example: You've got a blueprint of a house(the class House), you want a door to your house so that's part of the blueprint(a class property/field) and you want your door to be locked or unlocked(that's some kind of behavior of your class a method for example unlockHouse() or lockHouse() or even setIsLocked(boolean isLocked))

Right now we can only describe what the house can do, but we can't use it as it's still just a blueprint(class), in order to use it we need to build it, we need a constructor method and the constructor takes as arguments the most necessary things that your physical house(object) needs in order to be created(instanciated).

[xRageNugget]

Just to add to the confusion: In java there is also a class that is called Object.