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public class Student {

    private String name;

    private Integer age;

    // 全参构造函数

    public Student(String name, Integer age) {

        this.name = name;

        this.age = age;

    }

    public String getName() {

        return name;

    }

    public Integer getAge() {

        return age;

    }

    // toString 方法

    @Override

    public String toString() {

        return"Student{" + "name='" + name + '\'' + ", age=" + age + '}';

    }

}

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public class OptionalTest {

    public static void main(String[] args) {

        Student student = new Student("Bob", 18);

        Optional<Student> studentOpt = Optional.ofNullable(student);

    }

}

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// 编写方法 1

if (student == null) {

    return UNKNOWN_STUDENT;

} else {

    return student;

}

// 编写方法 2

if (!studentOpt.isPresent()) {

    return UNKNOWN_STUDENT;

} else {

    return studentOpt.get();

}

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// if 语句

if (student!= null) {

    System.out.println(student);

}

// Optional

studentOpt.ifPresent(System.out::println);

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// if 语句

if (student == null) {

    return UNKNOWN_STUDENT; // 或抛出异常

} else {

    return student;

}

// Optional

return studentOpt.orElse(UNKNOWN_STUDENT);

return studentOpt.orElseThrow(RuntimeException::new);

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// if 语句

if (student == null) {

    return UNKNOWN_STUDENT;

} else {

    return generateWithFunction();

}

// Optional

return studentOpt.orElseGet(() -> generateWithFunction());

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// Java 7

if (student!= null) {

    String name = student.getName();

    if (name!= null) {

        return name;

    } else {

        return null;

    }

} else {

    return null;

}

// Java 8

return studentOpt.map(Student::getName).orElse(null);