java函数式编程之Consumer

参考https://blog.csdn.net/z345434645/article/details/53794724

　　https://blog.csdn.net/chuji2012/article/details/77871011

1、先来看一个简单的Consumer<T>的例子

描述：Consumer< T>接口接受一个T类型参数，没有返回值。

源码如下：

public interface Consumer<T> {

    /**
     * Performs this operation on the given argument.
     *
     * @param t the input argument
     */
    void accept(T t);
}

测试代码如下：

@Test
public void test(){
    UserT userT = new UserT("zm");
    //接受一个参数
    Consumer<UserT> userTConsumer = userT1 -> userT1.setName("zmChange");};
    userTConsumer.accept(userT);
    logger.info(userT.getName());//输出zmChange
}

java8以前的实现如下：

@Test
public void test1(){
    UserT userT = new UserT("zm");
    this.change(userT);
    logger.info(userT.getName());//输出zmChange
}

private void change(UserT userT){
    userT.setName("zmChange");
}

2、Predicate和Consumer综合应用

为了详细说明Predicate和Consumer接口，通过一个学生例子：Student类包含姓名、分数以及待付费用，每个学生可根据分数获得不同程度的费用折扣。

Student类源代码：

public class Student {

    String firstName;
    String lastName;
    Double grade;
    Double feeDiscount = 0.0;
    Double baseFee = 2000.0;

    public Student(String firstName, String lastName, Double grade) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.grade = grade;
    }

    public void printFee(){
        Double newFee = baseFee - ((baseFee * feeDiscount)/100);
        System.out.println("The fee after discount: " + newFee);
    }
}

然后分别声明一个接受Student对象的Predicate接口以及Consumer接口的实现类。本例子使用Predicate接口实现类的test()方法判断输入的Student对象是否拥有费用打折的资格，然后使用Consumer接口的实现类更新输入的Student对象的折扣。

public class PredicateConsumerDemo {

    public static Student updateStudentFee(Student student, Predicate<Student> predicate, Consumer<Student> consumer){
        if (predicate.test(student)){
            consumer.accept(student);
        }
        return student;
    }

}

Predicate和Consumer接口的test()和accept()方法都接受一个泛型参数。不同的是test()方法进行某些逻辑判断并返回一个boolean值，而accept()接受并改变某个对象的内部值。updateStudentFee方法的调用如下所示：

public class Test {
    public static void main(String[] args) {
        Student student1 = new Student("Ashok","Kumar", 9.5);

        student1 = updateStudentFee(student1,
                //Lambda expression for Predicate interface
                student -> student.grade > 8.5,
                //Lambda expression for Consumer inerface
                student -> student.feeDiscount = 30.0);
        student1.printFee(); //The fee after discount: 1400.0

        Student student2 = new Student("Rajat","Verma", 8.0);
        student2 = updateStudentFee(student2,
                //Lambda expression for Predicate interface
                student -> student.grade >= 8,
                //Lambda expression for Consumer inerface
                student -> student.feeDiscount = 20.0);
        student2.printFee();//The fee after discount: 1600.0

    }
}