java - 生成方法未识别变量

我在无参数构造函数SandBox sb中创建了AsteroidGame()，但是当我尝试向sb添加对象时，在我的generate方法中找不到变量SandBox。对我要去哪里错有任何见解吗？

    public static void main(String[] args)
    {
        new AsteroidGame();
    }

    public AsteroidGame()
    {
        //Create SandBox
        SandBox sb = new SandBox();
        sb.init(this);
    }

    public void generate()
    {
        //Instantiate Rocket and add it to Sandbox
        Dimension dime = sb.getPanelBounds();
        Rocket rock = new Rocket(dime.width/2, dime.height/2);
        sb.addBlob(rock);
}

最佳答案

您可以这样做Declare SandBox as instance/class variable：

    SandBox sb; // Declare SandBox as instance/class variable
    public static void main(String[] args)
        {
            new AsteroidGame();
        }

        public AsteroidGame()
        {
            //Create SandBox
            sb = new SandBox();
            sb.init(this);
        }

        public void generate()
        {
            //Instantiate Rocket and add it to Sandbox
            Dimension dime = sb.getPanelBounds();
            Rocket rock = new Rocket(dime.width/2, dime.height/2);
            sb.addBlob(rock);
    }

或Create a new local variable in generate（）method:

public static void main(String[] args)
    {
        new AsteroidGame();
    }

    public AsteroidGame()
    {
        //Create SandBox
        SandBox sb = new SandBox();
        sb.init(this);
    }

    public void generate()
    {
        // Create a new local variable here
        SandBox sb = new SandBox();
        Dimension dime = sb.getPanelBounds();
        Rocket rock = new Rocket(dime.width/2, dime.height/2);
        sb.addBlob(rock);
}

关于java - 生成方法未识别变量，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/28935409/