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接口，Comparable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;		
}


}