Purpose of a constructor in Java?

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Constructors are used to initialize the instances of your classes. You use a constructor to create new objects often with parameters specifying the initial state or other important information about the object

From the official Java tutorial:

A class contains constructors that are invoked to create objects from the class blueprint. Constructor declarations look like method declarations—except that they use the name of the class and have no return type. For example, Bicycle has one constructor:

public Bicycle(int startCadence, int startSpeed, int startGear) {
    gear = startGear;
    cadence = startCadence;
    speed = startSpeed;
}

To create a new Bicycle object called myBike, a constructor is called by the new operator:

Bicycle myBike = new Bicycle(30, 0, 8);

new Bicycle(30, 0, 8) creates space in memory for the object and initializes its fields.

Although Bicycle only has one constructor, it could have others, including a no-argument constructor:

public Bicycle() {
gear = 1;
cadence = 10;
speed = 0;
}

Bicycle yourBike = new Bicycle(); invokes the no-argument constructor to create a new Bicycle object called yourBike.

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