java基础理论Stream管道流Map操作示例

List<String> alpha = Arrays.asList( "Monkey" , "Lion" , "Giraffe" , "Lemur" );

//不使用Stream管道流

List<String> alphaUpper = new ArrayList<>();

for (String s : alpha) {

     alphaUpper.add(s.toUpperCase());

}

System.out.println(alphaUpper); //[MONKEY, LION, GIRAFFE, LEMUR]

// 使用Stream管道流

List<String> collect = alpha.stream().map(String::toUpperCase).collect(Collectors.toList());

//上面使用了方法引用，和下面的lambda表达式语法效果是一样的

//List<String> collect = alpha.stream().map(s -> s.toUpperCase()).collect(Collectors.toList());

System.out.println(collect); //[MONKEY, LION, GIRAFFE, LEMUR]

List<Integer> lengths = alpha.stream()

         .map(String::length)

         .collect(Collectors.toList());

System.out.println(lengths); //[6, 4, 7, 5]

Stream.of( "Monkey" , "Lion" , "Giraffe" , "Lemur" )

         .mapToInt(String::length)

         .forEach(System.out::println);

public static void main(String[] args){

     Employee e1 = new Employee( 1 , 23 , "M" , "Rick" , "Beethovan" );

     Employee e2 = new Employee( 2 , 13 , "F" , "Martina" , "Hengis" );

     Employee e3 = new Employee( 3 , 43 , "M" , "Ricky" , "Martin" );

     Employee e4 = new Employee( 4 , 26 , "M" , "Jon" , "Lowman" );

     Employee e5 = new Employee( 5 , 19 , "F" , "Cristine" , "Maria" );

     Employee e6 = new Employee( 6 , 15 , "M" , "David" , "Feezor" );

     Employee e7 = new Employee( 7 , 68 , "F" , "Melissa" , "Roy" );

     Employee e8 = new Employee( 8 , 79 , "M" , "Alex" , "Gussin" );

     Employee e9 = new Employee( 9 , 15 , "F" , "Neetu" , "Singh" );

     Employee e10 = new Employee( 10 , 45 , "M" , "Naveen" , "Jain" );

     List<Employee> employees = Arrays.asList(e1, e2, e3, e4, e5, e6, e7, e8, e9, e10);

     /*List<Employee> maped = employees.stream()

             .map(e -> {

                 e.setAge(e.getAge() + 1);

                 e.setGender(e.getGender().equals("M")?"male":"female");

                 return e;

             }).collect(Collectors.toList());*/

     List<Employee> maped = employees.stream()

             .peek(e -> {

                 e.setAge(e.getAge() + 1 );

                 e.setGender(e.getGender().equals( "M" )? "male" : "female" );

             }).collect(Collectors.toList());

     System.out.println(maped);

}

List<String> words = Arrays.asList( "hello" , "word" );

words.stream()

         .map(w -> Arrays.stream(w.split( "" )))    //[[h,e,l,l,o],[w,o,r,l,d]]

         .forEach(System.out::println);

java.util.stream.ReferencePipeline$Head @3551a94

java.util.stream.ReferencePipeline$Head @531be3c5

words.stream()

         .flatMap(w -> Arrays.stream(w.split( "" ))) // [h,e,l,l,o,w,o,r,l,d]

         .forEach(System.out::println);