Step 6 of 6

Several objects

One class can make as many objects as a program needs, and each object keeps its own state: calling a method on one of them never changes the others. The values for new objects often come from the user:

Main.java

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("First plant:");
        String first = scanner.nextLine();
        System.out.println("Second plant:");
        String second = scanner.nextLine();

        Plant left = new Plant(first, 10);
        Plant right = new Plant(second, 10);
        left.grow(8);
        right.grow(3);
        left.cut(12);
        left.printInfo();
        right.printInfo();
    }
}

Plant.java

public class Plant {
    private String name;
    private int height;

    public Plant(String name, int height) {
        this.name = name;
        this.height = height;
    }

    public void printInfo() {
        System.out.println(this.name + ", " + this.height + " cm");
    }

    public void grow(int cm) {
        this.height = this.height + cm;
    }

    public void cut(int cm) {
        this.height = this.height - cm;
        if (this.height < 5) {
            this.height = 5;
        }
    }
}

Input

mint
basil

Output

First plant:
Second plant:
mint, 6 cm
basil, 13 cm

left and right are built from the same class, with names read from the user, and each has its own name and height.
left.grow(8) and left.cut(12) change only left: the variable in front of the dot decides which object a method works on. right only grew by 3.

A program can use as many classes as it needs, each in its own file next to Main.java, and main can make objects of all of them: a garden program could have a Plant class and a Lamp class, and create a few of each. Module 19 shows how to keep any number of objects in a list.

Several objects

Your task

Challenge 2

Challenge 3