java8(Stream)-案例练习-9

心已赠人 2022-11-10 10:46 249阅读 0赞

/* * 文件名：StreamTest * 版权：Copyright by 启海云仓 qihaiyun.com * 描述： * 创建人：Administrator * 创建时间：2019/9/29 * 修改理由： * 修改内容： */
    package Stream_2.stream案例练习;
    
    import Entity.Employee;
    import org.junit.Before;
    import org.junit.Test;
    
    import java.util.Arrays;
    import java.util.List;
    import java.util.Optional;
    
    /** * 〈一句话简述该类/接口的功能〉 * 〈功能详细描述〉 * * @author Administrator * @version 1.0 * @see StreamTest * @since JDK1.8 */
    public class StreamTest { 
        List<Employee> list = Employee.addEmployees();
        List<Transaction> transactions = null;
    
        /* 1. 给定一个数字列表，如何返回一个由每个数的平方构成的列表呢？给定【1，2，3，4，5】， 应该返回【1，4，9，16，25】。 */
        @Test
        public void test1() { 
            List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);
            list.stream().map(x -> x * x).forEach(System.out::println);
        }
    
        /* 2. 怎样用 map 和 reduce 方法数一数流中有多少个Employee呢？ */
    
        @Test
        public void test2() { 
            Optional<Integer> reduce = list.stream().map(e -> 1).reduce(Integer::sum);
            System.out.println(reduce);
        }
    
        /* 3. 查找所有来自剑桥的交易员，并按姓名排序 */
        @Test
        public void test3() { 
            transactions.stream()
                    .map(Transaction::getTrader)
                    .filter(trader -> trader.getCity().equals("Cambridge"))
                    .sorted((t1, t2) -> t1.getName().compareTo(t2.getName()))
                    .forEach(System.out::println);
        }
    
        /* 4. 返回所有交易员的姓名字符串，按字母顺序排序 */
        @Test
        public void test4() { 
            transactions.stream()
                    .map(Transaction::getTrader)
                    .map(Trader::getName)
                    .sorted();
        }
    
        /* 5.有没有交易员在Milan工作的 */
        @Test
        public void test5() { 
            boolean inMilan = transactions.stream()
                    .anyMatch(t -> t.getTrader().getCity().equals("Milan"));
        }
    
        /* 6. 打印生活在剑桥Cambridge的交易员的所有交易额 */
        @Test
        public void test6() { 
            transactions.stream()
                   .filter(transaction -> transaction.getTrader().getCity().equals("Cambridge"))
                    .map(Transaction::getValue)
                    .forEach(System.out::println);
        }
    
        /* 7. 所有交易中，最高的交易额是多少 */
        @Test
        public void test7() { 
            Optional<Integer> max = transactions.stream()
                    .map(transaction -> transaction.getValue())
                    .max(Integer::compareTo);
            System.out.println(max);
        }
    
        /* 8. 找到交易额最小的交易 */
        @Test
        public void test8() { 
            Optional<Integer> min = transactions.stream()
                    .map(transaction -> transaction.getValue())
                    .min(Integer::compareTo);
            System.out.println(min);
        }
    
        @Before
        public void before() { 
            Trader raoul = new Trader("Raoul", "Cambridge");
            Trader mario = new Trader("Mario", "Milan");
            Trader alan = new Trader("Alan", "Cambridge");
            Trader brian = new Trader("Brian", "Cambridge");
    
            transactions = Arrays.asList(
                    new Transaction(brian, 2011, 300),
                    new Transaction(raoul, 2012, 1000),
                    new Transaction(raoul, 2011, 400),
                    new Transaction(mario, 2012, 710),
                    new Transaction(mario, 2012, 700),
                    new Transaction(alan, 2012, 950)
            );
        }
    
    }
    
    
    //交易员
    class Trader { 
    
        private String name;
        private String city;
    
        public Trader() { 
        }
    
        public Trader(String name, String city) { 
            this.name = name;
            this.city = city;
        }
    
        public String getName() { 
            return name;
        }
    
        public void setName(String name) { 
            this.name = name;
        }
    
        public String getCity() { 
            return city;
        }
    
        public void setCity(String city) { 
            this.city = city;
        }
    
        @Override
        public String toString() { 
            return "Trader [name=" + name + ", city=" + city + "]";
        }
    
    }
    
    
    //交易
    class Transaction { 
    
        private Trader trader;
        private int year;
        private int value;
    
        public Transaction() { 
        }
    
        public Transaction(Trader trader, int year, int value) { 
            this.trader = trader;
            this.year = year;
            this.value = value;
        }
    
        public Trader getTrader() { 
            return trader;
        }
    
        public void setTrader(Trader trader) { 
            this.trader = trader;
        }
    
        public int getYear() { 
            return year;
        }
    
        public void setYear(int year) { 
            this.year = year;
        }
    
        public int getValue() { 
            return value;
        }
    
        public void setValue(int value) { 
            this.value = value;
        }
    
        @Override
        public String toString() { 
            return "Transaction [trader=" + trader + ", year=" + year + ", value="
                    + value + "]";
        }
    
    }