package com.qiku.day18; import java.util.ArrayList; import java.util.Arrays; import java.util.List; public class Zuo01 { public static void main(String[] args) { //1、产生10个1-100的随机数,并放到一个数组中, //把数组中大于等于10的数字放到一个list集合中,并打印到控制台。 int[] arr = new int[10]; for (int i = 0; i < arr.length; i++) { arr[i] = (int) (Math.random()*99+1); } System.out.println(Arrays.toString(arr)); List<Integer> list = new ArrayList<>(); for (int i = 0; i < arr.length; i++) { if (arr[i] >= 10){ list.add(arr[i]); } } System.out.println(list); } }
package com.qiku.day18; import java.util.*; public class Zuo02 { public static void main(String[] args) { //2、已知数组存放一批QQ号码,QQ号码最长为11位,最短为5位 //String[] strs ={"12345","67891","12347809933","98765432102","67891","12347809933"}。 // 将该数组里面的所有qq号都存放在LinkedList中,将list中重复元素删除, // 将list中所有元素分别用迭代器和增强for循环打印出来。 String[] strs ={"12345","67891","12347809933","98765432102","67891","12347809933"}; Set<String> set = new HashSet<>(); for (int i = 0; i < strs.length; i++) { set.add(strs[i]); } System.out.println(set); List<String> list = new LinkedList<>(); Iterator<String> it = set.iterator(); while (it.hasNext()){ list.add(it.next()); } System.out.println("迭代器:"+list); System.out.print("增强for循环:"); for (String str: list){ System.out.print(" "+str); } } }
package com.qiku.day18; public class Student implements Comparable<Student>{ private String name; private int age; private float score; public Student(String name, int age, float score) { this.name = name; this.age = age; this.score = score; } @Override public int compareTo(Student o) { if (this.score == o.score){ return this.age - o.age; } return o.score - this.score > 0 ? 1 : -1; } @Override public String toString() { return "Student{" + "name='" + name + '\'' + ", age=" + age + ", score=" + score + '}'; } 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 float getScore() {return score;} public void setScore(float score) {this.score = score;} }
package com.qiku.day18; import java.util.ArrayList; import java.util.Collection; import java.util.Collections; import java.util.List; public class Zuo03 { public static void main(String[] args) { //3、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。 Student stu1 = new Student("liusan", 20, 90); Student stu2 = new Student("lisi",22,90); Student stu3 = new Student("wangwu",20,99); Student stu4 = new Student("sunliu",22,100); List<Student> list = new ArrayList<>(); list.add(stu1); list.add(stu2); list.add(stu3); list.add(stu4); System.out.println(list); Collections.sort(list); System.out.println(list); } }
package com.qiku.day18; import java.util.*; public class Zuo04 { public static void main(String[] args) { Map<Integer, String> map = new HashMap<Integer, String>(); map.put(1, "张三丰"); map.put(2, "周芷若"); map.put(3, "汪峰"); map.put(4, "灭绝师太"); System.out.println(map); map.put(5,"李晓红"); map.remove(1);//根据key删除元素 map.put(2,"周林"); System.out.println(map); System.out.println("============"); //1 Set<Integer> keys = map.keySet(); Iterator<Integer> itKey = keys.iterator(); while (itKey.hasNext()){ Integer key = itKey.next(); String value = map.get(key); System.out.println(key+":"+value); } //2 Collection<String> values = map.values(); Iterator<String> valueIt = values.iterator(); while (valueIt.hasNext()){ String value = valueIt.next(); System.out.println(value); } //3 通过遍历所有的enter 遍历map // Set < Map.Entry < Integer,String > > entries = map.entrySet(); Iterator<Map.Entry<Integer,String>>entryIt = entries.iterator(); while (entryIt.hasNext()){ Map.Entry<Integer,String> entry = entryIt.next(); Integer key = entry.getKey(); String value = entry.getValue(); System.out.println(key+":"+value); } } }
package com.qiku.day18; import java.util.ArrayList; import java.util.Iterator; import java.util.List; import java.util.Map; public class Zuo05 { public static void main(String[] args) { /** * 5、已知有十六支男子足球队参加2020 奥运会。写一个程序,把这16 支球队随机分为4 个组。 * 采用List集合和随机数 * 2020 奥运会男足参赛国家: * 科特迪瓦,阿根廷,澳大利亚,塞尔维亚,荷兰,尼日利亚、日本,美国,中国, * 新西 兰,巴西,比利时,韩国,喀麦隆,洪都拉斯,意大利 */ String[] strs = {" 科特迪瓦","阿根廷","澳大利亚","塞尔维亚","荷兰","尼日利亚","日本","美国" , "中国","新西兰","巴西","比利时","韩国","喀麦隆","洪都拉斯","意大利"}; List<String> list1 = new ArrayList<>(); List<String> list2 = new ArrayList<>(); List<String> list3 = new ArrayList<>(); List<String> list4 = new ArrayList<>(); List<String> list = new ArrayList<>(); for (int i = 0; i < strs.length; i++) { list.add(strs[i]); } System.out.println(list); for (int i = 0;i < strs.length;i++){ int index = (int) (Math.random()*list.size()); if(i<4){ list1.add(list.get(index)); list.remove(list.get(index)); } if(i>=4 && i<8){ list2.add(list.get(index)); list.remove(list.get(index)); } if(i>=8 && i<12){ list3.add(list.get(index)); list.remove(list.get(index)); } if(i>=12 && i<16){ list4.add(list.get(index)); list.remove(list.get(index)); } } System.out.println(list1); System.out.println(list2); System.out.println(list3); System.out.println(list4); } }