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package com.jcfc.stream.map;
import com.jcfc.lambda.entity.Employee;
import org.junit.Test;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.stream.Stream;
/**
* 二、映射：
* map: 接收Lambda，将元素转换成其它形式或提取信息。接受一个函数作为参数，该函数会被应用到每个元素上，并将其映射成一个新的元素
* flatMap:接收一个函数作为参数，将流中的每个值都转换成另一个流，然后把所有流连接成一个流
*
*/
public class MapStream {
private List<Employee> emps = Arrays.asList(
new Employee("张三", 18, 3333.33),
new Employee("李四", 38, 5555.55),
new Employee("王五", 28, 6666.66),
new Employee("赵六", 58, 9999.99),
new Employee("田七", 8, 7777.77)
);
List<String> list = Arrays.asList("aaa","bbb","ccc","ddd","eee");
@Test
public void test() {
list.stream()
// .map((str) -> str.toUpperCase())
.map(String::toUpperCase)
.forEach(System.out::println);
}
@Test
public void test2() {
emps.stream()
// .map((e) -> e.getName())
.map(Employee::getName)//只有一个参数，第一个参数是实例方法的调用者，实例方法参数为空，也可以使用ClassName::method
.forEach(System.out::println);
}
@Test
public void test3() {
Stream<Stream<Character>> stream = list.stream()
.map(MapStream::filterCharacter);
stream.forEach((sm) -> {
sm.forEach(System.out::println);
});
}
//把集合中每一个字符串转换成一个字符流
private static Stream<Character> filterCharacter(String str) {
List<Character> list = new ArrayList<>();
for (Character ch : str.toCharArray()) {
list.add(ch);
}
return list.stream();
}
@Test
public void test4() {
Stream<Character> stream = list.stream()
.flatMap(MapStream::filterCharacter);
stream.forEach(System.out::println);
}
}