Lambda_13 函数表达式 Stream map reduce聚合计算方法

╰+哭是因爲堅強的太久メ 2022-11-20 04:53 99阅读 0赞

### Stream reduce聚合计算方法 ###

1.  通常于map搭配使用 map 提取需要统计的数据
2.  reduce聚合计算方法 进行统计

代码示例：

public class Lambda14 { 
        public static void main(String[] args) { 
            List<Student> students = Arrays.asList(new Student("张三", 18),
                    new Student("李四", 19),
                    new Student("王五", 21),
                    new Student("赵六", 22));
    
            /** * 内部类实现stream reduce */
            Integer sumAge = students.stream().map(stu -> stu.getAge()).reduce(new BinaryOperator<Integer>() { 
                @Override
                public Integer apply(Integer i1, Integer i2) { 
                    System.out.println("i1:" + i1 + ",i2:" + i2);
                    return i1 + i2;
                }
            }).get();
            System.out.println("内部类实现stream reduce");
            System.out.println(sumAge);
    
    
            /** * Lambda实现stream reduce */
            System.out.println("Lambda实现stream reduce");
            Integer sumAgelambda = students.stream().map(Student::getAge).reduce((i1, i2) -> i1 + i2).get();
            System.out.println(sumAgelambda);
        }
    }
    
    class Student { 
        private String name;
        private Integer age;
    
        public Student(String name, Integer age) { 
            this.name = name;
            this.age = age;
        }
    
        public String getName() { 
            return name;
        }
    
        public void setName(String name) { 
            this.name = name;
        }
    
        public Integer getAge() { 
            return age;
        }
    
        public void setAge(Integer age) { 
            this.age = age;
        }
    
        @Override
        public String toString() { 
            return "Student{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    }

输出：

内部类实现stream reduce
    i1:18,i2:19
    i1:37,i2:21
    i1:58,i2:22
    80
    Lambda实现stream reduce
    80