day16_课后练习题

第1题

案例：

​ 1、用一个String[]数组存点数

​ 2、用一个String[]数组存花色

​ 3、用一个String[]数组存大王、小王

​ 4、用上面的数组，生成一副扑克牌

​ 5、遍历显示全副扑克牌

​ 6、模拟给4个人随机发牌，每个人11张牌

​ 7、显示每个人的牌和剩余的牌

​ 效果如下：

package com.atguigu.test01;import java.util.ArrayList;
import java.util.Random;public class Test01 {public static void main(String[] args) {String[] dian = {"A","2","3","4","5","6","7","8","9","10","J","Q","K"};String[] hua = {"黑桃","红桃","方片","梅花"};String[] wang = {"大王","小王"};ArrayList<String> list = new ArrayList<String>();for (int i = 0; i < dian.length; i++) {for (int j = 0; j < hua.length; j++) {list.add(hua[j]+dian[i]);}}for (int i = 0; i < wang.length; i++) {list.add(wang[i]);}for (int i = 0; i < list.size(); i++) {System.out.print(list.get(i)+"  ");if((i+1)%10==0){System.out.println();}}System.out.println();System.out.println("发牌：");Random rand = new Random();ArrayList<String> one = new ArrayList<String>();for (int i = 0; i < 11; i++) {one.add(list.remove(rand.nextInt(list.size())));}ArrayList<String> two = new ArrayList<String>();for (int i = 0; i < 11; i++) {two.add(list.remove(rand.nextInt(list.size())));}ArrayList<String> three = new ArrayList<String>();for (int i = 0; i < 11; i++) {three.add(list.remove(rand.nextInt(list.size())));}ArrayList<String> four = new ArrayList<String>();for (int i = 0; i < 11; i++) {four.add(list.remove(rand.nextInt(list.size())));}System.out.println("第1个人：" + one);System.out.println("第2个人：" + two);System.out.println("第3个人：" + three);System.out.println("第4个人：" + four);System.out.println("剩余：" + list);}
}

第2题

• 模拟乐透号码。

  • 随机生成10个号码放到集合中，范围1-50，作为乐透号码。不能重复。
  • 键盘录入10个整数放到集合中，范围1-50，不能重复。
  • 录入的整数与乐透号码对比，统计猜中了几个。

• 代码实现，效果如图所示：

  

开发提示：

• 当使用集合时，可以通过contains方法，判断某集合中是否包含某元素

package com.atguigu.test02;import java.util.ArrayList;
import java.util.Random;
import java.util.Scanner;public class Test02 {public static void main(String[] args) {ArrayList<Integer> lotNumList = lotNum();System.out.println("乐透号码已经生成,游戏开始:");ArrayList<Integer> inputList = inputNum();System.out.println("您输入的号码为:"+inputList);int count  =  countNum(inputList , lotNumList);System.out.println("乐透号码为:"+lotNumList);System.out.println("猜中了:"+count+"个数字");}public static int countNum(ArrayList<Integer> inputList, ArrayList<Integer> lotNumList) {int  count  = 0;for (int i = 0; i < inputList.size(); i++) {Object num  = inputList.get(i);if (lotNumList.contains(num)){count++;}}return count ;}public static ArrayList<Integer> inputNum(){ArrayList<Integer> list = new ArrayList<Integer>();Scanner sc = new Scanner(System.in);for (int i = 0; i < 10; ) {System.out.println("请输入第"+(i+1)+"个数字[1-50]:");int num  = sc.nextInt();if (num >=1 && num<=50 && !list.contains(num)){list.add(num);i++;}else{System.out.println(num+"超过[1-50]范围或重复录入，数字无效，请重新输入");}}sc.close();return list;}public static ArrayList<Integer> lotNum(){ArrayList<Integer> list = new ArrayList<Integer>();Random r = new Random();for (int i = 0; i < 10; ) {int num  = r.nextInt(50) + 1;if (!list.contains(num)){list.add(num);i++;}}return list;}
}

第3题

案例：

​ 1、随机生成10个[1,100]之间的整数，放到List集合中，遍历显示

​ 2、找出前3名最大值，删除它们，注意可能重复

​ 3、显示删除后的结果

​ 效果如下：

package com.atguigu.test03;import java.util.ArrayList;
import java.util.Random;public class Test03 {public static void main(String[] args) {ArrayList<Integer> nums = getNum();System.out.println("10个随机值：" + nums);ArrayList<Integer> maxList = getTop3(nums);System.out.println("前3个最大的：" + maxList);System.out.println("删除后：" + nums);}public static ArrayList<Integer> getNum() {ArrayList<Integer> list = new ArrayList<Integer>();Random r = new Random();for (int i = 0; i < 10; i++) {int n = r.nextInt(100) + 1;list.add(n);}return list;}public static ArrayList<Integer> getTop3(ArrayList<Integer> list){ArrayList<Integer> maxList = new ArrayList<Integer>();for (int i = 0; i < 3; i++) {Integer max = (Integer) list.get(0);for (int j = 0; j < list.size(); j++) {Integer num = (Integer) list.get(j);if(max < num){max = num;}}maxList.add(max);while(list.contains(max)){list.remove(max);}}return maxList;}}

第4题

• 随机生成30个数，范围2-100，获取其中的质数。
• 代码实现，效果如图所示：

开发提示：

• 质数：在一个大于1的整数中，除了1和此整数自身外，没法被其他自然数整除的数。

package com.atguigu.test04;import java.util.ArrayList;
import java.util.Random;public class Test04 {public static void main(String[] args) {ArrayList<Integer> ranNum = getRanNum();System.out.println("随机数为:");System.out.println(ranNum);System.out.println("其中的质数为:");ArrayList<Integer> pNum = getPNum(ranNum);System.out.println(pNum);}public static ArrayList<Integer> getPNum(ArrayList<Integer> ranNum) {ArrayList<Integer> list = new ArrayList<Integer>();for (int i = 0; i < ranNum.size(); i++) {Integer integer = (Integer) ranNum.get(i);if (isP(integer)) {list.add(integer);}}return list;}public static ArrayList<Integer> getRanNum() {Random random = new Random();ArrayList<Integer> list = new ArrayList<Integer>();for (int i = 0; i < 30; i++) {list.add(random.nextInt(99) + 2);}return list;}public static boolean isP(int n) {boolean isPrime = true;for (int i = 2; i < n; i++) {if (n % i == 0) {isPrime = false;break;}}return isPrime;}
}

第5题

案例：

​ 1、请定义方法public static int listTest(Collection list,String s)统计集合中指定元素出现的次数

​ 2、创建集合，集合存放随机生成的30个小写字母

​ 3、用listTest统计，某些元素的出现次数

​ 4、效果如下

package com.atguigu.test05;import java.util.ArrayList;
import java.util.Collection;
import java.util.Random;public class Test05 {public static void main(String[] args) {ArrayList<String> list = new ArrayList<String>();Random rand = new Random();for (int i = 0; i < 30; i++) {list.add((char)(rand.nextInt(26)+97)+"");}System.out.println(list);System.out.println("a:"+listTest(list, "a"));	System.out.println("b:"+listTest(list, "b"));	System.out.println("c:"+listTest(list, "c"));System.out.println("x:"+listTest(list, "x"));	}public static int listTest(Collection<String> list, String string) {int count = 0;for (String object : list) {if(string.equals(object)){count++;}}return count;}
}

第6题

案例：键盘录入一个字符串，去掉其中重复字符，打印出不同的那些字符，必须保证顺序。例如输入：aaaabbbcccddd，打印结果为：abcd。效果如图：

提示：LinkedHashSet的使用

package com.atguigu.test06;import java.util.LinkedHashSet;
import java.util.Scanner;public class Test06 {public static void main(String[] args) {Scanner input = new Scanner(System.in);System.out.print("请输入一串字母：");String str = input.nextLine();System.out.println("str=" + str);LinkedHashSet<Character> set = new LinkedHashSet<Character>();for (int i = 0; i < str.length(); i++) {set.add(str.charAt(i));}System.out.print("去重后：");String result = "";for (Character object : set) {result += object;}System.out.println(result);}
}

第7题

案例：双色球规则：双色球每注投注号码由6个红色球号码和1个蓝色球号码组成。红色球号码从1—33中选择；蓝色球号码从1—16中选择；请随机生成一注双色球号码。（要求同色号码不重复）

开发提示：可以使用TreeSet和ArrayList结合

package com.atguigu.test07;import java.util.ArrayList;
import java.util.Random;
import java.util.TreeSet;public class Test07 {public static void main(String[] args) {TreeSet<Integer> red = new TreeSet<Integer>();Random rand = new Random();while(red.size()<6){red.add(rand.nextInt(33)+1);}ArrayList<Integer> list = new ArrayList<Integer>();list.addAll(red);list.add(rand.nextInt(16)+1);//蓝色号码System.out.println("双色球所有号码：" + list);System.out.print("红色号码：");for (int i = 0; i < list.size()-1; i++) {System.out.print(list.get(i)+" ");}System.out.println("蓝色号码：" + list.get(list.size()-1));}
}

第8题

案例：有如下四个学生的成绩：

（1）用Comparable接口对下列四位同学的成绩做降序排序，如果成绩一样，那在成绩排序的基础上按照年龄由小到大排序。

（2）用Comparator实现按照姓名排序

（3）效果如下

package com.atguigu.test08;import java.util.Comparator;
import java.util.TreeSet;public class Test08 {public static void main(String[] args) {System.out.println("按照成绩和年龄排序：");TreeSet<Student> set = new TreeSet<Student>();set.add(new Student("liusan",20,90.0));set.add(new Student("lisi",22,90.0));set.add(new Student("wangwu",20,99.0));set.add(new Student("sunliu",22,100.0));for (Object object : set) {System.out.println(object);}System.out.println("按照姓名排序：");TreeSet<Student> all = new TreeSet<Student>(new Comparator<Student>() {@Overridepublic int compare(Student o1, Student o2) {return o1.getName().compareTo(o2.getName());}});for (Student object : set) {all.add(object);}for (Student object : all) {System.out.println(object);}}
}
class Student implements Comparable<Student>{private String name;private int age;private double score;public Student(String name, int age, double score) {super();this.name = name;this.age = age;this.score = score;}public Student() {super();}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public double getScore() {return score;}public void setScore(double score) {this.score = score;}@Overridepublic String toString() {return "Student [name=" + name + ", age=" + age + ", score=" + score + "]";}@Overridepublic int compareTo(Student o) {if(this.getScore()>o.getScore()){return -1;}else if(this.getScore() < o.getScore()){return 1;}return this.getAge() - o.getAge();}}