why constructor is same name in our field?

Every class has a constructor which is named the same as the class. You specify what is required to instantiate(create a object of that class) in the constructor. In this example, in order to create a PezDispenser object, you will have to pass the characterName value as specified in the the PezDispenser's constructor. For example, this is how you would create a PezDispenser object when you add the characterName value into the constructor:

PezDispenser newDispenser = PezDispenser("DarthVader");

If you left the constructor without characterName, you would create the object like this:

PezDispenser newDispenser = PezDispenser();

A constructor is the main attributes of the object that creates an object from the template. Look at a class as a play-dough mold, and the variables it takes in is the play-dough, creating an object (the instance). Without the constructor, instances cant be made. The class itself is not an object, but a blueprint on making that object. the instances are the objects. So in other classes, i can make as many playdough molds as i please and use them separately as seperate objects of the same class, because of the constructor.

public class PlayDoughStar {

private String starColor;

public PlayDoughStar(String starColor) {
     this.starColor= starColor;
} 
//the rest of the class code
}

so in a different class, i want to make a play-dough star:

public class Table {
PlayDoughStar redStar = new PlaydoughStar("red");
PlayDoughStar blueStar = new PlaydoughStar("blue");
//Tables constructor here {
//}