Stream流
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
/**
目标：初步体验Stream流的方便与快捷
*/
public class StreamTest {
public static void main(String[] args) {
List<String> names = new ArrayList<>();
Collections.addAll(names, "张三丰","张无忌","周芷若","赵敏","张强");
System.out.println(names);
//
// // 1、从集合中找出姓张的放到新集合
// List<String> zhangList = new ArrayList<>();
// for (String name : names) {
// if(name.startsWith("张")){
// zhangList.add(name);
// }
// }
// System.out.println(zhangList);
//
// // 2、找名称长度是3的姓名
// List<String> zhangThreeList = new ArrayList<>();
// for (String name : zhangList) {
// if(name.length() == 3){
// zhangThreeList.add(name);
// }
// }
// System.out.println(zhangThreeList);
// 3、使用Stream实现的
names.stream().filter(s -> s.startsWith("张")).filter(s -> s.length() == 3).forEach(s -> System.out.println(s));
}
}
import java.util.*;
import java.util.stream.Stream;
/**
目标：Stream流的获取
Stream流式思想的核心：
是先得到集合或者数组的Stream流（就是一根传送带）
然后就用这个Stream流操作集合或者数组的元素。
然后用Stream流简化替代集合操作的API.
集合获取流的API:
(1) default Stream<E> stream();
小结：
集合获取Stream流用: stream();
数组：Arrays.stream(数组) / Stream.of(数组);
*/
public class StreamDemo02 {
public static void main(String[] args) {
/** --------------------Collection集合获取流------------------------------- */
Collection<String> list = new ArrayList<>();
Stream<String> s = list.stream();
/** --------------------Map集合获取流------------------------------- */
Map<String, Integer> maps = new HashMap<>();
// 键流
Stream<String> keyStream = maps.keySet().stream();
// 值流
Stream<Integer> valueStream = maps.values().stream();
// 键值对流（拿整体）
Stream<Map.Entry<String,Integer>> keyAndValueStream = maps.entrySet().stream();
/** ---------------------数组获取流------------------------------ */
String[] names = {"赵敏","小昭","灭绝","周芷若"};
Stream<String> nameStream = Arrays.stream(names);
Stream<String> nameStream2 = Stream.of(names);
}
}
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Stream;
/**
目标：Stream流的常用API
forEach : 逐一处理(遍历)
count：统计个数
-- long count();
filter : 过滤元素
-- Stream<T> filter(Predicate<? super T> predicate)
limit : 取前几个元素
skip : 跳过前几个
map : 加工方法
concat : 合并流。
*/
public class StreamDemo03 {
public static void main(String[] args) {
List<String> list = new ArrayList<>();
list.add("张无忌");
list.add("周芷若");
list.add("赵敏");
list.add("张强");
list.add("张三丰");
list.add("张三丰");
// Stream<T> filter(Predicate<? super T> predicate)
list.stream().filter(s -> s.startsWith("张")).forEach(s -> System.out.println(s));
long size = list.stream().filter(s -> s.length() == 3).count();
System.out.println(size);
// list.stream().filter(s -> s.startsWith("张")).limit(2).forEach(s -> System.out.println(s));
list.stream().filter(s -> s.startsWith("张")).limit(2).forEach(System.out::println);
list.stream().filter(s -> s.startsWith("张")).skip(2).forEach(System.out::println);
// map加工方法: 第一个参数原材料 -> 第二个参数是加工后的结果。
// 给集合元素的前面都加上一个：黑马的：
list.stream().map(s -> "黑马的：" + s).forEach(a -> System.out.println(a));
// 需求：把所有的名称 都加工成一个学生对象。
list.stream().map(s -> new Student(s)).forEach(s -> System.out.println(s));
// list.stream().map(Student::new).forEach(System.out::println); // 构造器引用 方法引用
// 合并流。
Stream<String> s1 = list.stream().filter(s -> s.startsWith("张"));
Stream<String> s2 = Stream.of("java1", "java2");
// public static <T> Stream<T> concat(Stream<? extends T> a, Stream<? extends T> b)
Stream<String> s3 = Stream.concat(s1 , s2);
s3.distinct().forEach(s -> System.out.println(s));
}
}
public class Employee {
private String name;
private char sex;
private double salary;
private double bonus;
private String punish; // 处罚信息
public Employee(){
}
public Employee(String name, char sex, double salary, double bonus, String punish) {
this.name = name;
this.sex = sex;
this.salary = salary;
this.bonus = bonus;
this.punish = punish;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public char getSex() {
return sex;
}
public void setSex(char sex) {
this.sex = sex;
}
public double getSalary() {
return salary;
}
public void setSalary(double salary) {
this.salary = salary;
}
public double getBonus() {
return bonus;
}
public void setBonus(double bonus) {
this.bonus = bonus;
}
public String getPunish() {
return punish;
}
public void setPunish(String punish) {
this.punish = punish;
}
public double getTotalSalay(){
return salary * 12 + bonus;
}
@Override
public String toString() {
return "Employee{" +
"name='" + name + '\'' +
", sex=" + sex +
", salary=" + salary +
", bonus=" + bonus +
", punish='" + punish + '\'' +
'}'+"\n";
}
}
import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Stream;
public class StreamDemo04 {
public static double allMoney ;
public static double allMoney2 ; // 2个部门去掉最高工资，最低工资的总和
public static void main(String[] args) {
List<Employee> one = new ArrayList<>();
one.add(new Employee("猪八戒",'男',30000 , 25000, null));
one.add(new Employee("孙悟空",'男',25000 , 1000, "顶撞上司"));
one.add(new Employee("沙僧",'男',20000 , 20000, null));
one.add(new Employee("小白龙",'男',20000 , 25000, null));
List<Employee> two = new ArrayList<>();
two.add(new Employee("武松",'男',15000 , 9000, null));
two.add(new Employee("李逵",'男',20000 , 10000, null));
two.add(new Employee("西门庆",'男',50000 , 100000, "被打"));
two.add(new Employee("潘金莲",'女',3500 , 1000, "被打"));
two.add(new Employee("武大郎",'女',20000 , 0, "下毒"));
// 1、开发一部的最高工资的员工。（API）
// 指定大小规则了
// Employee e = one.stream().max((e1, e2) -> Double.compare(e1.getSalary() + e1.getBonus(), e2.getSalary() + e2.getBonus()))
// .get();
// System.out.println(e);
Topperformer t = one.stream().max((e1, e2) -> Double.compare(e1.getSalary() + e1.getBonus(), e2.getSalary() + e2.getBonus()))
.map(e -> new Topperformer(e.getName(), e.getSalary() + e.getBonus())).get();
System.out.println(t);
// 2、统计平均工资，去掉最高工资和最低工资
one.stream().sorted((e1, e2) -> Double.compare(e1.getSalary() + e1.getBonus(), e2.getSalary() + e2.getBonus()))
.skip(1).limit(one.size() - 2).forEach(e -> {
// 求出总和：剩余员工的工资总和
allMoney += (e.getSalary() + e.getBonus());
});
System.out.println("开发一部的平均工资是：" + allMoney / (one.size() - 2));
// 3、合并2个集合流，再统计
Stream<Employee> s1 = one.stream();
Stream<Employee> s2 = two.stream();
Stream<Employee> s3 = Stream.concat(s1 , s2);
s3.sorted((e1, e2) -> Double.compare(e1.getSalary() + e1.getBonus(), e2.getSalary() + e2.getBonus()))
.skip(1).limit(one.size() + two.size() - 2).forEach(e -> {
// 求出总和：剩余员工的工资总和
allMoney2 += (e.getSalary() + e.getBonus());
});
// BigDecimal
BigDecimal a = BigDecimal.valueOf(allMoney2);
BigDecimal b = BigDecimal.valueOf(one.size() + two.size() - 2)