集合中按照商品价格排序，按照学生编号排序，Collections集合里的sort方法，Comparator<T>接口，Comparable<T>接口，

Collections 有一个sort方法，查看API文档

学生类：

public class Product implements Comparable<Product>{
private int p_id;
private String p_name;
private float price;

public Product(int p_id, String p_name, float price) {
super();
this.p_id = p_id;
this.p_name = p_name;
this.price = price;
}

public int compareTo(Product o) {
if(this.p_id>o.p_id) return 1;
else if(this.p_id<o.p_id) return -1;
else return 0;
}

}

测试类 按照学生id排序
public class Product implements Comparable<Product>{
private int p_id;
private String p_name;
private float price;

public Product(int p_id, String p_name, float price) {
super();
this.p_id = p_id;
this.p_name = p_name;
this.price = price;
}

public int compareTo(Product o) {
if(this.p_id>o.p_id) return 1;
else if(this.p_id<o.p_id) return -1;
else return 0;
}

}