JAVASE速通复习(二)
6 常见算法
6.1 排序算法
6.1.1 冒泡排序
核心就是每次从数组中找出最大值放到数组最后
import java.util.Arrays;public class test6 {public static void main(String[] args) {int [] arr = {5,2,3,1};//定义一个循环，控制排几轮for (int i = 0; i < 3; i++) {//定义一个循环每轮控制几次for (int j = 0; j < arr.length - i - 1; j++) {//如果大就交换if(arr[j] > arr[j+1]){int temp = arr[j];arr[j] = arr[j+1];arr[j+1] = temp;}}}System.out.println(Arrays.toString(arr));}
}
6.1.2 选择排序
核心是每轮选择当前位置，开始找出后边的较小值与该位置交换//其实就是选了最小的值放到了第一个位置。和冒泡排序不同的是，冒泡是两两比较，而比较的是定好位置比较
import java.util.Arrays;public class test7 {public static void main(String[] args) {int arr[] = {5,1,3,2};for (int i = 0; i < arr.length - 1; i++) {//控制几轮for (int j = i + 1; j < arr.length; j++) {if(arr[i] > arr[j]) {int temp = arr[i];arr[i] = arr[j];arr[j] = temp;}}}System.out.println(Arrays.toString(arr));}
}
6.1.3 二分查找*（有序）
public class test10 {public static void main(String[] args) {int arr[] = {7,23,79,81,103,127,256};System.out.println(binarySearch(arr, 81));}public static int binarySearch(int[] arr, int target) {int l = 0,r = arr.length-1;while(l<=r) {int mid = (l+r)/2;if(arr[mid]==target) {return mid;}else if(arr[mid]>target) {r = mid-1;}else{l = mid+1;}}return -1;}
}
7 正则表达式
7.1 概述
7.2 demo校验qq号是否合法
手写程序校验
public class demo1
{public static void main(String[] args) {System.out.println(checkQQ(null));System.out.println(checkQQ("4723897428478"));}public static boolean checkQQ(String qq){if(qq == null || qq.startsWith("0") || qq.length() < 6 || qq.length() > 20){return false;}//判断每个字符是否是数字for (int i = 0; i < qq.length(); i++) {char ch = qq.charAt(i);if(ch < '0' || ch > '9'){return false;}}return true;}
}
使用正则表达式
public static boolean checkQQ1(String qq){return qq != null && qq.matches("[1-9]\\d{5,19}");}7.3 书写规则
带中括号的内容只能匹配单个字符
预定义字符也只能匹配单个字符
切记不能出现中文
补充：
7.4 应用案例
7.4.1 验证手机号
package randomdemo;/** @author SHOWY*/import java.util.Scanner;public class phonedemo {public static void main(String[] args) {}public static void checkPhone(String phone){System.out.println("请输入你的电话号码");Scanner scanner = new Scanner(System.in);String phoneNum = scanner.nextLine();//13387383763 010-343434343434if(phoneNum.matches("1[3-9]\\d{9} | 0\\d{2,7}-?[1-9]\\d{4,19}")){System.out.println("您输入的号码格式正确");}else{System.out.println("您输入的号码格式不正确");}}
}
7.4.2 验证邮箱
public static void checkEmail(String mail){System.out.println("请输入你的电话邮箱");Scanner scanner = new Scanner(System.in);String mailnum = scanner.nextLine();//dsadasdasd@qq.com dashjdasdjh@qq.com.cnif(mailnum.matches("\\w{2,}@\\w{2,20}(\\.\\w{2,10}){1,2}")){System.out.println("您输入的邮箱格式正确");}else{System.out.println("您输入的邮箱格式不正确");}}7.5 正则表达式在一段内容中爬取信息
package randomdemo;/** @author SHOWY*/import java.util.regex.Matcher;
import java.util.regex.Pattern;public class demonew {public static void main(String[] args) {method1();}public static void method1() {String data = "电话 18827636726 18656455678" +"或者联系邮箱 dfhjkahds@qq.com" +"或者座机电话 010-98787898";//1.定义爬取规则String regex = "(\\w{2,}@\\w{2,20}(\\.\\w{2,10}){1,2}|(1[3-9]\\d{9}|0\\d{2,7}-?[1-9]\\d{4,19}))";//2.把正则表达式封装成一个pattern对象Pattern pattern = Pattern.compile(regex);//3.通过pattern对象去获取查找内容的匹配器对象Matcher matcher = pattern.matcher(data);//4.通过一个循环开始爬信息while (matcher.find()) {String rs = matcher.group();//获取到了找到的内容了System.out.println(rs);}}
}
7.6 用于搜索替换分割内容
注意这里s2.split（）返回的是字符串的数组
8 异常
8.1 认识异常
8.2 处理方式
8.3 自定义异常
8.3.1 自定义运行时异常demo
import com.sun.corba.se.impl.resolver.SplitLocalResolverImpl;public class TestE {public static void main(String[] args) {try {saveAge(160);} catch (Exception e) {e.printStackTrace();System.out.println("底层出现了问题");}}public static void saveAge(int age){if(age > 0 && age < 150){System.out.println("年龄保存成功" + age);}else{throw new AgeIllegalRuntimeException("年龄非法，你的年龄是" + age);}}
}
public class AgeIllegalRuntimeException extends RuntimeException {public AgeIllegalRuntimeException() {}public AgeIllegalRuntimeException(String message) {super(message);}
}
8.3.2 自定义编译时异常demo
其实差不多的，只是更强烈，要求你一定去处理一下，你可以往上抛，方法+throws+ 这个异常
8.4 异常的处理
8.4.1 第一种处理
8.4.2 第二种处理
9 集合框架
9.1 Collection的集合特点 
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;public class TestCollection {public static void main(String[] args) {ArrayList<String> list = new ArrayList<>();//有序 可重复有索引list.add("java1");list.add("java2");list.add("java1");list.add("java2");System.out.println(list.get(1));System.out.println(list);HashSet<String> set = new HashSet<>();//无序 不重复无索引set.add("java1");set.add("java2");set.add("java1");set.add("java2");set.add("java3");System.out.println(set);}
}
9.2 Collection常见方法
红框部分的操作是把集合转成了指定格式的数组
addAll方法可以把一个集合的数据倒入到另一个之中去
9.3 Collection的遍历方式
9.3.1 迭代器
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;public class demo666 {public static void main(String[] args) {Collection<String> c = new ArrayList<>();c.add("a");c.add("b");c.add("c");c.add("d");//1.使用迭代器遍历集合//从集合对象中获取迭代器对象Iterator<String> it = c.iterator();while(it.hasNext()){//这个hashnet方法是调用迭代器String demo = it.next();System.out.println(demo);}}
}
9.3.2 增强for循环
public class demo666 {public static void main(String[] args) {Collection<String> c = new ArrayList<>();c.add("a");c.add("b");c.add("c");c.add("d");
//增加for循环既可以遍历数组又可以遍历集合for(String s : c){System.out.println(s);}}
}9.3.3 Lambda表达式遍历集合
9.4 案例遍历集合中的自定义对象
9.5 List集合
9.5.1 list集合特点和特有方法
9.5.2 遍历方式
9.5.3 ArrayList集合的底层原理
9.5.4 LinkedList集合的底层原理
9.6 Set集合
9.6.1 特点
9.6.2 HashSet集合的底层原理
注意：这里如果想要希望set集合认为2内容一样的对象是重复的
9.6.3 LinkedHashSet集合的底层原理
9.6.4 TreeSet集合底层原理
方式1 demo
方式2 demo
如果两种方式都有的话，TreeSet会就近选择自己自带的比较器对象进行排序
简化：
9.7 集合的并发修改异常问题
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.function.Consumer;public class demo666 {public static void main(String[] args) {List<String> list = new ArrayList<>();list.add("小李子1");list.add("小李子2");list.add("小李子3");list.add("小李子4");list.add("小子1");System.out.println(list);Iterator<String> it = list.iterator();while (it.hasNext()) {String name = it.next();if (name.contains("李")) {it.remove();//这个操作删除迭代器当前遍历的数据，每删除一个相当于底层做了一个i--}}System.out.println(list);}
}
如果以下这样是会报异常的
用增加for循环或者lambda表达式遍历集合不能解决这种并发修改异常的问题
10 Colletction的其他相关知识
10.1 前置知识：可变参数
10.2 collections工具类
10.3 综合案例
需要先来个Gamedemo主程序,创建一个room对象，然后后面写room类，room里必须有一副牌，所以先写card类
public class GameDemo {public static void main(String[] args) {//1.牌类//2，房间Room room = new Room();}
}
public class Card {private String number;private String color;//每张牌是有大小的private int size;//提供一个无参构造器public Card(){}public Card(String number, String color,int size) {this.number = number;this.size = size;this.color = color;}public String getNumber() {return number;}public void setNumber(String number) {this.number = number;}public String getColor() {return color;}public void setColor(String color) {this.color = color;}public int getSize() {return size;}public void setSize(int size) {this.size = size;}@Overridepublic String toString() {return color + number + " (" + size + ")";}
}
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;public class Room {//必须有一副牌private List<Card> allCards = new ArrayList<Card>();public Room(){//1.做出54张排，存入到集合Allcards里面//a. 点数 个数 类型确定String[] num = {"3","4","5","6","7","8","9","10","J","Q","K","2"};//b.花色String[] col = {"♣","♠","♦","♥"};//c.遍历点数，内部遍历花色int size = 0;//表示每张牌的大小for (String nums : num) {size ++;for (String colo : col) {//得到一张牌Card e = new Card(nums,colo,size);allCards.add(e);}}Card c2 = new Card("","🤡",++size);Card c1 = new Card("","🃏",++size);Collections.addAll(allCards,c2,c1);System.out.println("新牌" + allCards);}
}
做牌就做好了，接下来是开始洗牌 发牌 对牌排序等等
import java.util.*;public class Room {//必须有一副牌private List<Card> allCards = new ArrayList<Card>();public Room(){//1.做出54张排，存入到集合Allcards里面//a. 点数 个数 类型确定String[] num = {"3","4","5","6","7","8","9","10","J","Q","K","2"};//b.花色String[] col = {"♣","♠","♦","♥"};//c.遍历点数，内部遍历花色int size = 0;//表示每张牌的大小for (String nums : num) {size ++;for (String colo : col) {//得到一张牌Card e = new Card(nums,colo,size);allCards.add(e);}}Card c2 = new Card("","🤡",++size);Card c1 = new Card("","🃏",++size);Collections.addAll(allCards,c2,c1);System.out.println("新牌" + allCards);}//游戏启动方法public void start(){//1.洗牌Collections.shuffle(allCards);System.out.println("洗牌后" + allCards);//2.发牌，首先定义三个玩家List<Card> xiaohong = new ArrayList<>();List<Card> xiaomei = new ArrayList<>();List<Card> xiaoming = new ArrayList<>();for(int i = 0; i < allCards.size() - 3; i++){Card c = allCards.get(i);if(i % 3 == 0){xiaohong.add(c);}else if(i % 3 == 1){xiaomei .add(c);}else{xiaoming .add(c);}}//3.对三个玩家的牌进行排序sortcards(xiaomei);sortcards(xiaohong);sortcards(xiaoming);//4.看牌List<Card> lastthreecard = allCards.subList(allCards.size() - 3, allCards.size());//包前不包后xiaomei.addAll(lastthreecard);//地主牌扔进去sortcards(xiaomei);System.out.println("xiaohong:" + xiaohong);System.out.println("xiaomei:" + xiaomei);System.out.println("xiaoming:" + xiaoming);}
//对牌排序private void sortcards(List<Card> cards) {Collections.sort(cards, new Comparator<Card>() {@Overridepublic int compare(Card o1, Card o2) {return o1.getSize() - o2.getSize();//升序}});}
}
11 Map集合
11.1 简述
11.2 常用方法
11.3 遍历方式
11.3.1 键找值
import java.util.HashMap;
import java.util.Map;
import java.util.Set;public class BIANLIMAP {public static void main(String[] args) {Map<String , Double> map = new HashMap<>();map.put("A", 1.0);map.put("B", 2.0);map.put("C", 3.0);map.put("D", 4.0);map.put("E", 5.0);System.out.println(map);//1.获取map全部的键Set<String> keys = map.keySet();System.out.println(keys);for (String key : keys) {double value = map.get(key);System.out.println(key + value);}}
}
11.3.2 键值对
把每一组键值对封装成键值对对象
public class BIANLIMAP {public static void main(String[] args) {Map<String , Double> map = new HashMap<>();map.put("A", 1.0);map.put("B", 2.0);map.put("C", 3.0);map.put("D", 4.0); map.put("E", 5.0);System.out.println(map);Set<Map.Entry<String, Double>> entries = map.entrySet();for (Map.Entry<String, Double> entry : entries) {String key = entry.getKey();Double value = entry.getValue();System.out.println(key + ":" + value);}}
}
11.3.3 lambda表达式
import java.util.HashMap;
import java.util.Map;
import java.util.Set;public class BIANLIMAP {public static void main(String[] args) {Map<String , Double> map = new HashMap<>();map.put("A", 1.0);map.put("B", 2.0);map.put("C", 3.0);map.put("D", 4.0);map.put("E", 5.0);System.out.println(map);map.forEach((k,v) ->{System.out.println(k + "====>" + v);});}
}
11.3.4 案例
import java.util.*;public class lianxi {public static void main(String[] args) {List<String> data = new ArrayList<String>();String[] selects = {"A","B","C","D"};Random rand = new Random();for (int i = 0; i <=80; i++) {int index = rand.nextInt(4);//0 1 2 3data.add(selects[index]);}System.out.println(data);//统计每个景点的投票人数//准备一个map集合统计最终的结果Map<String,Integer> result = new HashMap<>();for (String s : data) {//问一下map集合是否存在该景点if(result.containsKey(s)){//说明统计过，其值+1，重新存入到mapresult.put(s,result.get(s) + 1);}else{result.put(s, 1);}}System.out.println(result);}
}
11.4 HashMap
如果是这样的话
import java.util.HashMap;
import java.util.Map;public class HashMapdemo {public static void main(String[] args) {Map<student,String> map = new HashMap<student,String>();map.put(new student("John",12),"John");map.put(new student("John",12),"John1");map.put(new student("tom",22),"John2");map.put(new student("jerry",28),"John3");System.out.println(map);}
}
他输出4个值，不会认为前两个是重复的键
所以重写一个equals,让其哈希值一样，就会只留一个元素
import java.util.Objects;public class student {String name;int age;public student(String name, int age) {this.name = name;this.age = age;}@Overridepublic boolean equals(Object object) {if (this == object) return true;if (object == null || getClass() != object.getClass()) return false;student student = (student) object;return age == student.age && Objects.equals(name, student.name);}@Overridepublic int hashCode() {return Objects.hash(name, age);}
}
11.5 LinkedHashMap
11.6 TreeMap
方式1
方式2
因为这个比较器对象离着这个集合更近，所以他会用比较器对象，所以是年龄的降序排序
12 补充：集合的嵌套
12.1 定义
集合中的元素又是一个集合
取值的话这么取
13 JDK8新特性
13.1 Stream
stream流支持链式编程
13.2 Stream流的使用步骤
13.3 获取stream流
如果要整体处理Map
13.4 stream流的中间方法
import javax.xml.crypto.dsig.spec.XSLTTransformParameterSpec;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.stream.Stream;public class StreamTest {public static void main(String[] args) {List<student> students = new ArrayList<>();student s1 = new student("lili2",26,172.5);student s2 = new student("lili2",26,172.5);student s3 = new student("lili3",23,167.6);student s4 = new student("lili4",25,169.0);student s5 = new student("lili5",35,183.8);student s6 = new student("lili6",34,168.5);Collections.addAll(students, s1, s2, s3, s4, s5, s6);//需求找出年龄大于等于23 且年龄小于等于30的并降序排序students.stream().filter(s -> s.getAge() >= 23 && s.getAge() <= 30).sorted((o1,o2) -> o2.getAge() - o1.getAge()).forEach(s -> System.out.println(s));//需求 取出身高最高的3名学生 并输出students.stream().sorted((o1,o2) -> Double.compare(o2.getHeight(),o1.getHeight())).limit(3).forEach(s -> System.out.println(s));//需求 取出身高倒数的2名学生 并输出students.stream().sorted((o1,o2) -> Double.compare(o2.getHeight(),o1.getHeight())).skip(students.size() - 2).forEach(s -> System.out.println(s));//需求 找出身高超过168的学生叫什么，要求去除重复的名字 再输出,map其实就是加工students.stream().filter(s -> s.getHeight() > 168).map(s -> s.getName()).distinct().forEach(s -> System.out.println(s));//distinct 去重复自定义类型的对象（希望内容一样就认为重复 重写hashcode和equals）students.stream().filter(s -> s.getHeight() > 167).distinct().forEach(s -> System.out.println(s));Stream<String> st1 = Stream.of("111", "222");Stream<String> st2 = Stream.of("112", "223");Stream<String> concat = Stream.concat(st1, st2);concat.forEach(s -> System.out.println(s));}
}
13.5 Stream流常见的终结方法
import javax.xml.crypto.dsig.spec.XSLTTransformParameterSpec;
import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;public class StreamTest {public static void main(String[] args) {List<student> students = new ArrayList<>();student s1 = new student("lili2", 26, 172.5);student s2 = new student("lili2", 26, 172.5);student s3 = new student("lili3", 23, 167.6);student s4 = new student("lili4", 25, 169.0);student s5 = new student("lili5", 35, 183.8);student s6 = new student("lili6", 34, 168.5);Collections.addAll(students, s1, s2, s3, s4, s5, s6);//需求 :计算超过168的学生有几人long count = students.stream().filter(s -> s.getHeight() > 168).count();System.out.println(count);//需求 :找出身高最高的学生对象，输出student student = students.stream().max((o1, o2) -> Double.compare(o1.getHeight(), o2.getHeight())).get();System.out.println(student);//需求: 找出身高高于170的学生对象，并放到一个新的集合中返回//流只能收集一次List<student> students1 = students.stream().filter(a -> a.getHeight() > 170).collect(Collectors.toList());System.out.println(students1);Set<student> students2 = students.stream().filter(a -> a.getHeight() > 170).collect(Collectors.toSet());//去重了System.out.println(students2);//需求: 找出身高高于170的学生对象，把学生对象的名字身高存入到一个map中Map<String, Double> students3 = students.stream().filter(s -> s.getHeight() > 170).distinct().collect(Collectors.toMap(a -> a.getName(), a -> a.getHeight()));System.out.println(students3);}
}