Java 8 : Stream API 练习

Posted 2020-10-04 Ipeter

//店铺属性类
public class Property {
	String  name;
    // 距离，单位:米
    Integer distance;
    // 销量，月售
    Integer sales;
    // 价格，这里简单起见就写一个级别代表价格段
    Integer priceLevel;
    public Property(String name, int distance, int sales, int priceLevel) {
        this.name = name;
        this.distance = distance;
        this.sales = sales;
        this.priceLevel = priceLevel;
    }
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public Integer getDistance() {
		return distance;
	}
	public void setDistance(Integer distance) {
		this.distance = distance;
	}
	public Integer getSales() {
		return sales;
	}
	public void setSales(Integer sales) {
		this.sales = sales;
	}
	public Integer getPriceLevel() {
		return priceLevel;
	}
	public void setPriceLevel(Integer priceLevel) {
		this.priceLevel = priceLevel;
	}
	@Override
	public String toString() {
		return "Property [name=" + name + ", distance=" + distance + ", sales=" + sales + ", priceLevel=" + priceLevel
				+ "]";
	}
    
}

　　

//JAVA8Stream它提供了对集合操作的增强  与I/O不同
public class TestJAVA8Stream {
public static void main(String[] args) {
	/*// Stream操作 List排序
	System.out.println("=====JAVA8Stream操作============方法1找到距离我最近的店铺");
	Property p1 = new Property("木桶饭", 1000, 500, 2);
    Property p2 = new Property("黄焖鸡", 2300, 1500, 3);
    Property p3 = new Property("麦当劳", 580, 3000, 1);
    Property p4 = new Property("肯德基", 6000, 200, 4);
    List<Property> properties = Arrays.asList(p1, p2, p3, p4);
	String name2 = properties.stream()
	                .sorted(Comparator.comparingInt(x -> x.distance))
	                .findFirst()
	                .get().name;
	System.out.println("距离我最近的店铺是:" + name2);*/
	/*System.out.println("======传统操作List排序===========方法二找到距离我最近的店铺");
	Property p1 = new Property("木桶饭", 1000, 500, 2);
    Property p2 = new Property("黄焖鸡", 2300, 1500, 3);
    Property p3 = new Property("麦当劳", 580, 3000, 1);
    Property p4 = new Property("肯德基", 6000, 200, 4);
    List<Property> properties = Arrays.asList(p1, p2, p3, p4);
    Collections.sort(properties, (x, y) -> x.distance.compareTo(y.distance));
    String name = properties.get(0).name;
    System.out.println("距离我最近的店铺是:" + name);*/
	System.out.println("=====迭代=======");
	Property p1 = new Property("木桶饭", 1000, 500, 2);
    Property p2 = new Property("黄焖鸡", 2300, 1500, 3);
    Property p3 = new Property("woi麦当劳", 580, 3000, 1);
    Property p4 = new Property("肯德基", 6000, 200, 4);
    List<Property> properties = Arrays.asList(p1, p2, p3, p4);
	int count = 0;//月销量大于1000的店铺个数
	for (Property property : properties) {
	    if(property.sales > 1000){
	        count++;
	    }
	}
	System.out.println("月销量大于1000的店铺个数:"+count);
	//使用内部迭代进行计算
	long count2 = properties.stream().filter(p -> p.sales > 1000).count();
	System.out.println("月销量大于1000的店铺个数:"+count2);
	long count3 =properties.stream().filter(p -> p.distance < 1000).count();//筛选出距离我在1000米内的店铺
	long count4 =properties.stream().filter(p -> p.name.length() > 5).count();//筛选出名称大于5个字的店铺
	Property property = properties.stream().max(Comparator.comparingInt(p -> p.priceLevel)).get();//筛选出价格最低的店铺
	//获取距离我最近的2个店铺
	List<Property> properties_s = properties.stream()
            .sorted(Comparator.comparingInt(x -> x.distance))
            .limit(2)
            .collect(Collectors.toList());
	//获取所有店铺的名称
	List<String> names = properties.stream()
            .map(p -> p.name)
            .collect(Collectors.toList());
	//获取每个店铺的价格等级
	Map<String, Integer> map = properties.stream()
	        .collect(Collectors.toMap(Property::getName, Property::getPriceLevel));
	//所有价格等级的店铺列表
	Map<Integer, List<Property>> priceMap = properties.stream()
            .collect(Collectors.groupingBy(Property::getPriceLevel));
	
	
	
}
}