java里null强转为某个类会报错吗?

Posted 2021-01-25 lizb0907

1.定义一个User类如下：

/**
 * @author lizhibiao
 * @date 2018/11/27 17:21
 */
public class User
{
    private String userName;

    private int age;

    private int cutScore;

    public String getUserName()
    {
        return userName;
    }

    public void setUserName(String userName)
    {
        this.userName = userName;
    }

    public int getAge()
    {
        return age;
    }

    public void setAge(int age)
    {
        this.age = age;
    }

    public int getCutScore() {
        return cutScore;
    }

    public void setCutScore(int cutScore) {
        this.cutScore = cutScore;
    }
}

2.测试null是否可以转为User类

public class Test
{
    public static void main(String[] args)
    {
        User user = (User)null;
        System.out.println(user);
    }
}

运行结果如下:

null

也就是输出值为null，所以null可以强转为某个类编译不报错，但是强转后还是为null

3.如果null来调用方法则会报错

public class Test
{
    public static void main(String[] args)
    {
        User user = (User)null;
        System.out.println(user.getUserName());
    }
}

运行结果如下：

Exception in thread "main" java.lang.NullPointerException

 at str.Test.main(Test.java:11)

报空异常