Java8中HashMap的性能提升與Stream在開發中的應用

Stream在開發中的應用

package com.wkcto.stream;

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.function.BinaryOperator;
import java.util.stream.Collectors;

/**
 * Author : 動力節點老崔
 */
public class Test03 {
    public static void main(String[] args) {
        //把Car小汽車的數據保存到List集合中
        List<Car> carshop = new ArrayList<>();
        carshop.add(new Car("Benz", false, 68, CarType.SUV));
        carshop.add(new Car("Audi", true, 28, CarType.HATCHBACK));
        carshop.add(new Car("BMW", false, 88, CarType.HATCHBACK));
        carshop.add(new Car("Geeley", true, 18, CarType.HATCHBACK));
        carshop.add(new Car("Xiali", true, 8, CarType.THREECOMPARTMENT));
        carshop.add(new Car("Haval", false, 18, CarType.SUV));
        carshop.add(new Car("Jeep", true, 38, CarType.SUV));
        carshop.add(new Car("Honda", false, 28, CarType.THREECOMPARTMENT));
        carshop.add(new Car("Chery", true, 18, CarType.THREECOMPARTMENT));
        carshop.add(new Car("Benz", false, 58, CarType.THREECOMPARTMENT));

        //1根據價格降序排序后,顯示汽車品牌
        carshop.stream()
                .sorted((c1,c2) -> c2.getPrice()-c1.getPrice())
                .map(Car::getBrand)
                .distinct()
                .forEach(System.out::println);
        System.out.println("---------------------");

        //2 找出已賣的車, 按價格升序排序
        carshop.stream()
                .filter(car -> car.isSold() )
                .sorted(Comparator.comparing(Car::getPrice))
                .forEach(System.out::println);
        System.out.println("---------------------");

        //3 查看有哪些車型
        carshop.stream()
                .map(car -> car.getType())
                .distinct()
                .forEach(System.out::println);
        System.out.println("---------------------");

        //4SUV型號的車有哪些
        List<Car> collect = carshop.stream()
                .filter(car -> car.getType() == CarType.SUV)
                .collect(Collectors.toList());
        System.out.println( collect );

        // 40萬以下的車的品牌, 排序
        carshop.stream()
                .filter(car -> car.getPrice() < 40)
                .map(Car::getBrand)
                .distinct()
                .sorted()
                .forEach(System.out::println);
        System.out.println("---------------------");

        //6)統計沒有賣出去的車的數量
        System.out.println( carshop.stream().filter(car -> !car.isSold()).count() );

        //7)判斷是否有Geeley品牌的汽車
        System.out.println( carshop.stream().anyMatch(car -> "Geeley".equals(car.getBrand())));

        //8)最貴的車的價格
        System.out.println(carshop.stream().map(Car::getPrice).reduce(Integer::max).get() );

        //9)顯示已賣出去最貴的車
        System.out.println( carshop.stream().filter(Car::isSold)
//            .reduce(BinaryOperator.maxBy((car1, car2)->(car1.getPrice()- car2.getPrice())))
               .collect(Collectors.maxBy(Comparator.comparing(Car::getPrice)))
                .get()
        );
    }
}

package com.wkcto.stream;

import java.util.Objects;

/**
 * Author : 動力節點老崔
 */
public class Car {
    private String brand;   //品牌
    private  boolean sold;  //是否已賣
    private int price;
    private CarType type;   //車型

    public Car(String brand, boolean sold, int price, CarType type) {
        this.brand = brand;
        this.sold = sold;
        this.price = price;
        this.type = type;
    }

    public Car() {
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Car car = (Car) o;
        return sold == car.sold &&
                price == car.price &&
                Objects.equals(brand, car.brand) &&
                type == car.type;
    }

    @Override
    public int hashCode() {
        return Objects.hash(brand, sold, price, type);
    }

    @Override
    public String toString() {
        return "Car{" +
                "brand='" + brand + '\'' +
                ", sold=" + sold +
                ", price=" + price +
                ", type=" + type +
                '}';
    }

    public String getBrand() {
        return brand;
    }

    public Car setBrand(String brand) {
        this.brand = brand;
        return this;
    }

    public boolean isSold() {
        return sold;
    }

    public Car setSold(boolean sold) {
        this.sold = sold;
        return this;
    }

    public int getPrice() {
        return price;
    }

    public Car setPrice(int price) {
        this.price = price;
        return this;
    }

    public CarType getType() {
        return type;
    }

    public Car setType(CarType type) {
        this.type = type;
        return this;
    }
}

package com.wkcto.stream;

/**
 * Author : 動力節點老崔
 */
public enum CarType {
    HATCHBACK, THREECOMPARTMENT,SUV
}

對HashMap性能的提升