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
 } }