Streams 过滤器
演示使用流的filter()，collect()，findAny()和orElse()
使用list过滤
public List<Student> getStudents(){
List<Student> result = new ArrayList<>();
result.add(new Student(1,"小易","21"));
result.add(new Student(2,"小二","23"));
result.add(new Student(4,"小思","24"));
result.add(new Student(3,"小三","24"));
return result;
}
public void StreamsFilterTest() {
List<Student> studentList = getFilterOutput(getStudents(), "小三");
System.out.println("把小三给我过滤掉====>"+studentList);
}
public List<Student> getFilterOutput(List<Student> liens ,String filter){
List<Student> result = new ArrayList<>();
for (Student student : liens) {
//过滤你想过滤掉的学生
if (!filter.equals(student.getName())){
result.add(student);
}
}
return result;
}
使用stream.filter()
stream.filter()来过滤List，并collect()以流转换为List
public void StreamsFilterTest() {
List<Student> studentList = getStudents().stream()
.filter(student -> !"小三".equals(student.getName()))
.collect(Collectors.toList());
studentList.forEach(student-> System.out.println("把小三给我剔除了---->"+student));
}
Streams filter(), findAny() and orElse()
1.8之前
public List<Student> getStudents(){
List<Student> result = new ArrayList<>();
result.add(new Student(1,"小易","21"));
result.add(new Student(2,"小二","23"));
result.add(new Student(4,"小思","24"));
result.add(new Student(3,"小三","24"));
return result;
}
public void StreamsFilterTest() {
Student studentByName = getStudentByName(getStudents(), "小三");
System.out.println(studentByName);
}
public Student getStudentByName(List<Student> students,String name){
Student student = null;
for (Student studentTemp : students) {
if (name.equals(studentTemp.getName())){
student = studentTemp;
}
}
return student;
}
1.8之后可以用
public List<Student> getStudents(){
List<Student> result = new ArrayList<>();
result.add(new Student(1,"小易","21"));
result.add(new Student(2,"小二","23"));
result.add(new Student(4,"小思","24"));
result.add(new Student(3,"小三","24"));
return result;
}
public void StreamsFilterTest() {
Student streamsFilterStudent = StreamsFilterStudent("小三");
System.out.println(streamsFilterStudent);
}
public Student StreamsFilterStudent(String name){
return getStudents().stream()
.filter(student -> name.equals(student.getName()))
.findAny()
.orElse(null);//如果没有返回null
}
多条件判断
public List<Student> getStudents(){
List<Student> result = new ArrayList<>();
result.add(new Student(1,"小易","21"));
result.add(new Student(2,"小二","23"));
result.add(new Student(4,"小二","24"));
result.add(new Student(3,"小二","24"));
return result;
}
public void StreamsFilterTest() {
Student streamsFilterStudent = StreamsFilterStudent();
System.out.println(streamsFilterStudent);
System.out.println("==============================");
System.out.println(StreamsFilterStudents());
}
public Student StreamsFilterStudent(){
return getStudents().stream()
.filter(student -> {
if (student != null && "24".equals(student.getAge())) {
return true;
}return false;
})
.findAny()
.orElse(null);//如果没有返回null
}
public Student StreamsFilterStudents(){
return getStudents().stream()
.filter(student -> {
if (student != null && "21".equals(student.getAge())) {
return true;
}
return false;
})
.findAny()
.orElse(null);//如果没有返回null
}
stream和map
如果使用map它返回的类型是Stirng
public List<Student> getStudents(){
List<Student> result = new ArrayList<>();
result.add(new Student(1,"小易","21"));
result.add(new Student(2,"小二","23"));
result.add(new Student(4,"小二","24"));
result.add(new Student(3,"小二","24"));
return result;
}
public void StreamsFilterTest() {
String studentName = StreamsFilterStudent("小二");
System.out.println("名字====>"+studentName);
}
public String StreamsFilterStudent(String name){
String studentName = getStudents().stream()
.filter(student -> name.equals(student.getName()))
.map(Student::getName)
.findAny()
.orElse(null);//如果没有返回null
System.out.println(studentName);
return studentName;
}
stream和list
public List<Student> getStudents(){
List<Student> result = new ArrayList<>();
result.add(new Student(1,"小易","21"));
result.add(new Student(2,"小二","23"));
result.add(new Student(4,"小二","24"));
result.add(new Student(3,"小二","24"));
return result;
}
public void StreamsFilterTest() {
List studentName = StreamsFilterStudent("小二");
System.out.println("名字====>"+studentName);
}
public List StreamsFilterStudent(String name){
List<String> studentList = getStudents().stream()
.map(Student::getName)
.limit(1)//可以指定返回多少条
.collect(Collectors.toList());
// studentList.forEach(s -> System.out.println(s));
studentList.forEach(System.out::println);
return studentList;
}
具体可参照oracle
https://www.oracle.com/technical-resources/articles/java/ma14-java-se-8-streams.html
并行流
打印数字 可以看到到时按照顺序排序打印下来的
public static void main(String[] args) {
System.out.println("normal");
IntStream range = IntStream.rangeClosed(1, 100);
range.forEach(System.out::println);
System.out.println("parallel");
IntStream intStream = IntStream.rangeClosed(1, 99);
intStream.forEach(System.out::println);
}
打印26个字母
public void getDataTest(){
List<String> data = getData();
data.stream().forEach(System.out::println);
}
public List<String> getData(){
List<String> data = new ArrayList<>();
int n = 97; //97=a 122=z
while (n<=122){
char c = (char) n;
data.add(String.valueOf(c));
n++;
}
return data;
}
Stream 是否以并行模式运行
可以是用paraller
public static void main(String[] args) {
System.out.println("normal");
IntStream range = IntStream.rangeClosed(1, 100);
range.forEach(System.out::println);
System.out.println("parallel");
IntStream intStream = IntStream.rangeClosed(1, 99);
IntStream parallel = intStream.parallel();
System.out.println(parallel.isParallel());//true为开启
parallel.forEach(System.out::println);
}
可加入线程名
public static void main(String[] args) {
System.out.println("normal");
IntStream range = IntStream.rangeClosed(1, 100);
range.forEach(p->{
System.out.println("Thread : "+ Thread.currentThread().getName() + " "+ p);
});
System.out.println("parallel");
IntStream intStream = IntStream.rangeClosed(1, 99);
IntStream parallel = intStream.parallel();
System.out.println(parallel.isParallel());//true为开启
parallel.forEach(p->{
System.out.println("Thread : "+Thread.currentThread().getName() + " "+ p);
});
}
public void getDataTest(){
List<String> data = getData();
data.stream().forEach(System.out::println);
}
public List<String> getData(){
List<String> data = new ArrayList<>();
int n = 97; //97=a 122=z
while (n<=122){
char c = (char) n;
data.add(String.valueOf(c));
n++;
}
return data;
}
待更新
