Java 比较器Comparator和Comparable的使用和区别
一、参考
二、知识点
1、使用场景:排序、分组
2、使用方法:
2.1 、Arrays.sort(T[],Comparator<? super T> c);
2.2、 Collections.sort(List<T> list,Comparator<? super T> c);
3、区别:
3.1 、Comparator相当于给一个数组或列表新增一种比较方式
3.2 、Comparable是接口需要被类继承的,相当于本身这个数组或者列表及类就有这种比较方式。后面有详细是有案例
三、案例
1、OrderBean订单类
1.1、继承了Comparable这个借口,有个简单的比较,升序的
//订单 public class OrderBean implements Comparable<OrderBean>{ private int id; //id private String cdate; //创建时间 private String product; //产品名称 private int weight; //重量 private long price; //价格 public OrderBean(int id, String cdate, String product, int weight, long price) { this.id = id; this.cdate = cdate; this.product = product; this.weight = weight; this.price = price; } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getCdate() { return cdate; } public void setCdate(String cdate) { this.cdate = cdate; } public String getProduct() { return product; } public void setProduct(String product) { this.product = product; } public int getWeight() { return weight; } public void setWeight(int weight) { this.weight = weight; } public long getPrice() { return price; } public void setPrice(long price) { this.price = price; } @Override public String toString() { return "\nOrder_"+id+": [" + "cdate="+cdate+", " + "product="+product+", " + "weight="+weight+" KG, " + "price="+price+" RMB, " + "]"; } /** * 按照weight升序 * sort的话默认调用 * */ public int compareTo(OrderBean o) { return weight - o.getWeight(); } }
2、Comparable接口使用
2.1、如果bean类继承Comparable接口,那么它的集合使用Collections.sort(list);可以默认调用bean类中复写的compareTo这个方法,进行排序
2.2、也可以使用compareTo单独比较两个类
private void testComparable() { System.out.println("\n\n testComparable()>>>"); OrderBean order1 = new OrderBean(1,"2018-01-01","牛肉",10,300); OrderBean order2 = new OrderBean(5,"2018-01-01","怪兽肉",80,400); OrderBean order3 = new OrderBean(2,"2018-02-01","牛肉",100,300); OrderBean order4 = new OrderBean(9,"2018-03-01","唐僧肉",2,600); List<OrderBean> list = new ArrayList<OrderBean>(); list.add(order1); list.add(order2); list.add(order3); list.add(order4); // weight升序排列 Collections.sort(list); System.out.println("按照订单的weight升序排列:" + list); System.out.println("比较1和3:"+order1.compareTo(order3)); }
testComparable()>>> 按照订单的weight升序排列:[ Order_9: [cdate=2018-03-01, product=唐僧肉, weight=2 KG, price=600 RMB, ], Order_1: [cdate=2018-01-01, product=牛肉, weight=10 KG, price=300 RMB, ], Order_5: [cdate=2018-01-01, product=怪兽肉, weight=80 KG, price=400 RMB, ], Order_2: [cdate=2018-02-01, product=牛肉, weight=100 KG, price=300 RMB, ]] 比较1和3:-90
3、Comparator比较器的使用
3.1、排序:大于、小于、等于
3.2、分组:等于、不等于
private void testComparator() { System.out.println("\n\n testComparator()>>>"); OrderBean order1 = new OrderBean(1,"2018-01-01","牛肉",10,300); OrderBean order2 = new OrderBean(5,"2018-01-01","怪兽肉",80,400); OrderBean order3 = new OrderBean(2,"2018-02-01","牛肉",100,300); OrderBean order4 = new OrderBean(9,"2018-03-01","唐僧肉",2,600); List<OrderBean> list = new ArrayList<OrderBean>(); list.add(order1); list.add(order2); list.add(order3); list.add(order4); /** * ----------------排列----------------- * 大于、小于、等于 * */ //id降序排列 Collections.sort(list, new Comparator<OrderBean>() { public int compare(OrderBean o1, OrderBean o2) { return o2.getId() - o1.getId(); } }); System.out.println("按照订单的id降序排列:"+list); //单价升序排列 Collections.sort(list, new Comparator<OrderBean>() { public int compare(OrderBean o1, OrderBean o2) { return (int)(o1.getPrice()/o1.getWeight() - o2.getPrice()/o2.getWeight()); } }); System.out.println("按照订单的单价升序排列:"+list); System.out.println("\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\"); /** * ----------------分组----------------- * 等于、不等于 * */ List<List<OrderBean>> byDate = divider(list,new Comparator<OrderBean>() { public int compare(OrderBean o1, OrderBean o2) { return o1.getCdate().equals(o2.getCdate()) ? 0:1; } }); for(int i=0;i<byDate.size();i++) { System.out.println("按照订单的cdate分组【"+i+"】:"+byDate.get(i)); } }
testComparator()>>> 按照订单的id降序排列:[ Order_9: [cdate=2018-03-01, product=唐僧肉, weight=2 KG, price=600 RMB, ], Order_5: [cdate=2018-01-01, product=怪兽肉, weight=80 KG, price=400 RMB, ], Order_2: [cdate=2018-02-01, product=牛肉, weight=100 KG, price=300 RMB, ], Order_1: [cdate=2018-01-01, product=牛肉, weight=10 KG, price=300 RMB, ]] 按照订单的单价升序排列:[ Order_2: [cdate=2018-02-01, product=牛肉, weight=100 KG, price=300 RMB, ], Order_5: [cdate=2018-01-01, product=怪兽肉, weight=80 KG, price=400 RMB, ], Order_1: [cdate=2018-01-01, product=牛肉, weight=10 KG, price=300 RMB, ], Order_9: [cdate=2018-03-01, product=唐僧肉, weight=2 KG, price=600 RMB, ]] \\\\\\\\\\\\\\\\\\ 按照订单的cdate分组【0】:[ Order_2: [cdate=2018-02-01, product=牛肉, weight=100 KG, price=300 RMB, ]] 按照订单的cdate分组【1】:[ Order_5: [cdate=2018-01-01, product=怪兽肉, weight=80 KG, price=400 RMB, ], Order_1: [cdate=2018-01-01, product=牛肉, weight=10 KG, price=300 RMB, ]] 按照订单的cdate分组【2】:[ Order_9: [cdate=2018-03-01, product=唐僧肉, weight=2 KG, price=600 RMB, ]]
分组工具方法
/** * @author wujn * @Description:按条件分组 * @param datas * @param c * 是否为同一组的判断标准 0 为同一组,1为不同组 * @return */ public static <T> List<List<T>> divider(Collection<T> datas, Comparator<? super T> c) { List<List<T>> result = new ArrayList<List<T>>(); for (T t : datas) { boolean isSameGroup = false; for (int j = 0; j < result.size(); j++) { if (c.compare(t, result.get(j).get(0)) == 0) { isSameGroup = true; result.get(j).add(t); break; } } if (!isSameGroup) { // 创建 List<T> innerList = new ArrayList<T>(); result.add(innerList); innerList.add(t); } } return result; }
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