如何优雅的解决空指针？

if(obj != null){
  //doSomthing
}
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public abstract class AbstractBook {

    //书名
    protected String bookName;

    //判断是否存在
    public abstract boolean isExist();

    //获取书名
    public abstract String getName();
}
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public class Book extends AbstractBook {

    public Book(String bookName) {
        this.bookName = bookName;
    }

    @Override
    public boolean isExist() {
        return false;
    }

    @Override
    public String getName() {
        return bookName;
    }
}
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public class NullObjectBook extends AbstractBook {

    @Override
    public boolean isExist() {
        return true;
    }

    @Override
    public String getName() {
        return "没有...";
    }
}
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public class BookFactory {

    public static final String[] names = {"java核心卷1", "java核心卷2", "软件随想录", "python入门"};

    public static AbstractBook getBook(String bookName){
        for (int i = 0; i < names.length; i++) {
            if(names[i].equals(bookName)){
                return new Book(bookName);
            }
        }
        return new NullObjectBook();
    }
}
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public class NullObjectClient {

    public static void main(String[] args) {
        AbstractBook book1 = BookFactory.getBook("java核心卷2");
        AbstractBook book2 = BookFactory.getBook("python入门");
        AbstractBook book3 = BookFactory.getBook("java编程思想");
        AbstractBook book4 = BookFactory.getBook("软件随想录");

        System.out.println(book1.getName());
        System.out.println(book2.getName());
        System.out.println(book3.getName());
        System.out.println(book4.getName());
    }
}
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java核心卷2
python入门
没有...
软件随想录
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Optional<Integer> possible = Optional.of(5);
possible.isPresent(); // returns true
possible.get(); // returns 5
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