java - 正确使用构造函数来更改 int 值？

Question

我有两个类。 1.主炮和2.枪。

枪:

public class Gun {
    private int ammoAmount = 15;
    public int getAmmoAmount() { //I believe this allows me to see the value of ammoAmount and use it in Main class.
        return ammoAmount; // Returns the value of ammoAmount to getAmmoAmount?
    }
    public Gun(int ammoUsage) { //this is the constructor right?
        ammoAmount = ammoAmount - ammoUsage; //Method that makes ammoAmount decrease by ammoUsage.
    }
    public void newAmmoAmount() {
        System.out.println("You have " + ammoAmount + " bullet(s) left."); // output of how much bullet is left.
    }
}

主要:

import java.util.Random;
public class Main {

    public static void main(String[] args) {

        Random rand = new Random();
        Gun fire1 = new Gun(0); // I need this to create an objective?
        fire1.newAmmoAmount(); // I need this for code below?
        int clip = fire1.getAmmoAmount(); // I need this to set clip for while loop?
        do { //starts loop
        int x = 5; //max # random can go to.
        int y = rand.nextInt(x); //Makes random integer from 0 to 5 for variable y.
        Gun fire = new Gun(y); //This is the objective that uses the constructor?
        System.out.println("You shot " + y + " bullet(s)."); //Print's out shots from random value y.
        fire.newAmmoAmount(); //uses method in Gun class?
        } while( clip > 0); //loops method till clip is less than 0.
    }
}

我尝试运行该程序，但它一直循环并且永远不会结束。 ammoAmount 的值不保存在 Gun 类中。如何才能更改不同类的 int 值？

我最近也有一个问题。我尝试按照他的说法使用构造函数。

How do I call a class into a class from main? and keep the output values?

但正如你所看到的，我并不是很成功。这只是我试图达到的一个更大概念的一个较小概念。所以基本上，我做对了构造函数吗？解决这个问题的方法是什么？

我在源代码中添加了一些注释，以向您展示我可能遇到的其他问题以及我是否也做了正确的事情。

Answer 1

你的“Gun”对象是不可变的 - 没有任何东西可以改变该对象的状态。此类类型有很多用途，但不太可能是您想要的。

听起来您想要“枪”的实例“开火”，因此“枪”实例中重命名子弹的数量会减少。当然，创建新的“枪”对象不会改变第一个对象中的子弹数量。

public class Gun {
    ...
    public fire(int ammoUsage) {
        ammoAmount = ammoAmount - ammoUsage; // TODO: add check for less than 0 
    }
}

使用此更新类，您可以开火直到没有子弹为止:

   int maxBulletsPerRound = 5; 
   Gun gun = new Gun(0); // fully loaded
   int clip;
   do {
    int numberOfBullets = rand.nextInt(maxBulletsPerRound); 
    gun.fire(numberOfBullets);
    System.out.println("You shot " + numberOfBullets + " bullet(s)."); 
    gun.newAmmoAmount(); //uses method in Gun class?
    clip = gun.getAmmoAmount(); // check how many bullets left
  } while( clip > 0); 

请注意，最好只使用 while(gun.getAmmoAmount() > 0)。