1. Stream
Case:4
public static void main(String[] args) {
List<String> citiesl =new ArrayList<>();
Collections.addAll(citiesl,"Nanjing City","Yangzhou City","Nanyang City","Changzhou City");
System.out.println(citiesl);//[Nanjing City, Yangzhou City, Nanyang City, Changzhou City]
//Method 1: Original method
List<String> citiesls =new ArrayList<>();
for (String s : citiesl) {
if (s.startsWith("南")){
citiesls.add(s);
}
}
System.out.println(citiesls);//[Nanjing City, Nanyang City]
//Method 2: Stream stream
List<String>ciiesl2=citiesl.stream().filter(c->c.startsWith("南")).collect(Collectors.toList());
System.out.println(ciiesl2);
}
2. Use of Stream stream
3. Case
public static void main(String[] args) {
//1, How to get the Stream stream of the List collection
List<String> citiesl =new ArrayList<>();
Collections.addAll(citiesl,"Nanjing City","Yangzhou City","Nanyang City","Changzhou City");
System.out.println(citiesl);
Stream<String> stream =citiesl.stream();
//2, How to obtain the Stream stream of the Set collection
Set<String> set =new HashSet<>();
Collections.addAll(set,"Nanjing City","Yangzhou City","Nanyang City","Changzhou City");
System.out.println(set);
Stream<String> stream1 =set.stream();
//3, How to obtain the Stream stream of the Map collection
Map<String,Integer> map =new HashMap<>();
map.put("coin",100);
map.put("Like",10);
map.put("Collection",20);
map.put("三连",1);
map.put(null,null);
System.out.println(map);
Set<String> keySet =map.keySet();
Stream<String> ks =keySet.stream();
Collection<Integer> values =map.values();
Stream<Integer> vs =values.stream();
Set<Map.Entry<String, Integer>> entries = map.entrySet();
Stream<Map.Entry<String, Integer>> stream2 = entries.stream();
stream2.filter(e ->e.getKey().contains("coin"))
.forEach(e ->System.out.println(e.getKey() + "-->" + e.getValue()));
//3, How to get the Stream stream of the array
String[] strings ={"A","B","C","D"};
Stream<String> s1 =Arrays.stream(strings);
Stream<String> s2 =Stream.of(strings);
}
4. Commonly used methods (key points)
Case:
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public static void main(String[] args) {
List<Double> scores =new ArrayList<>();
Collections.addAll(scores,88.2,95.3,12.5,65.7,99.5,44.2,35.6);
//Method 1, find data greater than or equal to 60, sort it, and then output it
scores.stream().filter(s -> s >=60).sorted().forEach(s-> System.out.println(s));
List<Shudent> shudents =new ArrayList<>();
Shudent s1 =new Shudent("Spider Spirit",26,160.0);
Shudent s2 =new Shudent("Supreme Treasure",25,176.0);
Shudent s3 =new Shudent("White Bone Essence",27,162.0);
Shudent s4 =new Shudent("Zixia",18,170.0);
Shudent s5 =new Shudent("牛魔王",68,180.0);
Collections.addAll(shudents,s1,s2,s3,s4,s5);
//Method 2, find the data whose age is greater than or equal to 23 and less than 30, sort it, and then output it
shudents.stream().filter(s -> s.getAge() >=23 & & s.getAge()<=30)
.sorted((o1,o2) -> o2.getAge() - o1.getAge())
.forEach(s-> System.out.println(s));
System.out.println("-----------------------------------------") ;
//Method 3, find the 3 oldest students and then output
shudents.stream().sorted((o1,o2) -> Double.compare(o2.getHeight(),o1.getHeight()))
.limit(3).forEach(s-> System.out.println(s));
System.out.println("-----------------------------------------") ;
//Method 4, find the three youngest students and output them
shudents.stream().sorted((o2,o1) -> Double.compare(o1.getHeight(),o2.getHeight()))
.skip(shudents.size()-2).forEach(s-> System.out.println(s));
System.out.println("-----------------------------------------") ;
//Method 5, find the names of several students whose height is over 170.0, remove duplicates, and then output
shudents.stream().filter(s -> s.getHeight() >=170.0).map(s->s.getNane())
.distinct()
.forEach(s-> System.out.println(s));
}
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package Map1;
public class Shudent {
private String nane;
private int age;
private double height;
@Override
public String toString() {
return "Shudent{" +
"nane='" + nane + ''' +
", age=" + age +
", height=" + height +
'}';
}
public Shudent(String nane, int age, double height) {
this.nane = nane;
this.age = age;
this.height = height;
}
public Shudent() {
}
public String getNane() {
return nane;
}
public void setNane(String nane) {
this.nane = nane;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public double getHeight() {
return height;
}
public void setHeight(double height) {
this.height = height;
}
}
5. Common termination methods in Stream streams
Case:
age Map1;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
public class MapTex6 {
public static void main(String[] args) {
List<Shudent> shudents =new ArrayList<>();
Shudent s1 =new Shudent("Spider Spirit",26,160.0);
Shudent s2 =new Shudent("Supreme Treasure",25,176.0);
Shudent s3 =new Shudent("White Bone Essence",27,162.0);
Shudent s4 =new Shudent("Zixia",18,170.0);
Shudent s5 =new Shudent("牛魔王",68,180.0);
Collections.addAll(shudents,s1,s2,s3,s4,s5);
//Method 1, calculate the number of students whose height exceeds 175.0, and output
long size = shudents.stream().filter(s -> s.getHeight() >=175.0).count();
System.out.println(size);
//Method 2, calculate the tallest student and output
Shudent s =shudents.stream().max((o2,o1) -> Double
.compare(o1.getHeight(),o2.getHeight())).get();
System.out.println(s);
//Method 3, calculate the student with the lowest height and output
Shudent ss =shudents.stream().min((o2,o1) -> Double
.compare(o1.getHeight(),o2.getHeight())).get();
System.out.println(ss);
//Method 4, calculate students whose height exceeds 175.0 and put them into a new collection
List <Shudent>shudents1=shudents.stream().filter(a -> a.getHeight() >=175.0)
.collect(Collectors.toList());
System.out.println(shudents1);
//Method 4, calculate students whose height exceeds 175.0. And put the name and height of the student object into a new collection
Map<String,Double>map=shudents.stream().filter(a -> a.getHeight() >=175.0)
.collect(Collectors.toMap(a->a.getNane(), a->a.getHeight()));
System.out.println(map);