/**
* StreamAPI的小练习
*/
public class StreamAPIExercise {
private List<Transaction>
transactions;
@Before
public void before() {
Trader yan =
new Trader("Yan", "Cambridge"
);
Trader zh =
new Trader("ZH", "Milan"
);
Trader rose =
new Trader("Rose", "Cambridge"
);
Trader lee =
new Trader("Lee", "Cambridge"
);
transactions = Arrays.asList(
new Transaction(yan, 2011, 300
),
new Transaction(zh, 2012, 1000
),
new Transaction(zh, 2011, 400
),
new Transaction(rose, 2012, 710
),
new Transaction(rose, 2012, 700
),
new Transaction(lee, 2012, 950
)
);
}
//给定一组数字的列表，返回由每个数字平方构成的列表
@Test
public void test1() {
Integer[] nums =
new Integer[]{1, 2, 3, 4, 5
};
Arrays.stream(nums).map((e) -> e *
e).forEach(System.out::println);
}
//使用map reduce 方法数出流中有多少个Employee
@Test
public void test2() {
Optional<Integer> sum = employees.stream().map(e -> 1
).reduce(Integer::sum);
System.out.println(sum.get());
}
List<Employee> employees =
Arrays.asList(
new Employee("Yan", 18, '男', 0
),
new Employee("Mike", 20, '女', 5000
),
new Employee("Lee", 18, '女', 8000
),
new Employee("Rose", 22, '男', 9000
),
new Employee("Sk", 30, '男', 11000
)
);
//找出2011年所有交易 并按照交易额排序（低->高）
@Test
public void test3() {
transactions.stream().filter((e) -> e.getYear() == 2011
)
//.sorted((t1, t2) -> Integer.compare(t1.getValue(), t2.getValue()))
.sorted(
new Comparator<Transaction>
() {
@Override
public int compare(Transaction o1, Transaction o2) {
return Integer.compare(o1.getValue(), o2.getValue());
}
})
.forEach(System.out::println);
}
//交易员都在哪些不同城市工作过
@Test
public void test4() {
transactions.stream().map(t ->
t.getTrader().getCity()).distinct().forEach(System.out::println);
}
//查找出来自剑桥的交易员，并按姓名排序
@Test
public void test5() {
transactions.stream().filter(t -> t.getTrader().getCity() == "Cambridge"
)
.map(t ->
t.getTrader().getName())
// .sorted((t1, t2) -> t1.compareTo(t2))
.distinct()
.sorted(new Comparator<String>
() {
@Override
public int compare(String o1, String o2) {
return o1.compareTo(o2);
}
})
.forEach(System.out::println);
}
//返回所有交易员姓名的字符串，并按字母顺序排序
@Test
public void test6() {
transactions.stream().map(t->
t.getTrader().getName())
.sorted().forEach(System.out::println);
System.out.println("------------------------------------------------"
);
//姓名连成一个字符串
System.out.println(transactions.stream().map(t ->
t.getTrader().getName())
.sorted().reduce(""
, String::concat));
System.out.println("------------------------------------------------"
);
//姓名连成一个字符串 并按照字母排序 并且忽略大小写
//思路：1.取出集合中每个姓名 2.对每个姓名 取出所有字符 存入list集合 3.list.stream 将stream sorted排序
transactions.stream().map(t ->
t.getTrader().getName())
.flatMap(StreamAPIExercise::filterCharacter)
.sorted((o1, o2) ->
o1.compareToIgnoreCase(o2))
.forEach(System.out::print);
}
public static Stream<String>
filterCharacter(String str) {
List<String> list =
new ArrayList<>
();
for (Character ch : str.toCharArray()) {
list.add(ch.toString());
}
return list.stream();
}
//有没有交易员在米兰工作
@Test
public void test7() {
boolean bl = transactions.stream().anyMatch(t -> t.getTrader().getCity() == "Milan"
);
}
//打印剑桥的交易员所有交易额
@Test
public void test8() {
Optional<Integer> sum = transactions.stream().filter(t -> t.getTrader().getCity().equals("Cambridge"
))
.map(t ->
t.getValue())
.reduce((x,y)->
Integer.sum(x,y));
// .reduce(Integer::sum);
System.out.println(sum);
}
//所有交易中最高的交易额是多少
@Test
public void test9() {
Optional<Integer> max = transactions.stream().map(t -> t.getValue()).max((x,y)->
Integer.compare(x,y));
System.out.println(max.get());
}
//找出最小交易
@Test
public void test10() {
Optional<Transaction> min = transactions.stream().min((x, y) ->
Integer.compare(x.getValue(), y.getValue()));
System.out.println(min.get());
}
}
转载于:https://www.cnblogs.com/MadYanYan/p/9942344.html
相关资源：尚硅谷-实验：Stream API练习.pdf
