JavaSE 集合 练习
1.某中学有若干学生(学生对象放在一个List中)，每个学生有一个姓名属性(String)、班级名称属性(String)和考试成绩属性(double)
某次考试结束后，每个学生都获得了一个考试成绩。遍历list集合，并把学生对象的属性打印出来
public class Student {public String name;
public String className;
public double score;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getClassName() {
return className;
}
public void setClassName(String className) {
this.className = className;
}
public double getScore() {
return score;
}
public void setScore(double score) {
this.score = score;
}
public Student() {
super();
// TODO Auto-generated constructor stub
}
public Student(String name, String className, double score) {
super();
this.name = name;
this.className = className;
this.score = score;
}
@Override
public String toString() {
return "Student [name=" + name + ", className=" + className + ", score=" + score + "]";
}
}
import java.util.ArrayList;
import java.util.List;
public class Test01 {
public static void main(String[] args) {
List<Student> list = new ArrayList<Student>();
list.add(new Student("tom","大数据",90));
list.add(new Student("jack","大数据",80));
list.add(new Student("lily","大数据",70));
list.add(new Student("lilei","大数据",60));
for (Student student : list) {
System.out.println(student);
}
}
}
.2编写程序，获取命令行参数中的字符串列表，输出其中重复的字符、不重复的字符以及消除重复以后的字符列表
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Scanner;
import java.util.Set;
import javax.swing.Spring;
public class Test02 {
public static Scanner sc = new Scanner(System.in);
public static Set<Character> s = new HashSet<Character>();//被消除后的数字
public static Set<Character> s2 = new HashSet<Character>();
public static List<Character> s3 = new ArrayList<Character>();//被消除的数字
public static void main(String[] args) {
System.out.println("请输入一串数字：");
List<String> list = new ArrayList<String>();
String str = sc.next();
char [] c = str.toCharArray();
for (int i = 0; i < c.length; i++) {
boolean b = s.add(c[i]);
if(!b){
s3.add(c[i]);
}
}
System.out.println("消除后数字为：");
for (char d : s) {
System.out.print(d);
}
System.out.println();
System.out.println("被消除的字符为：");
for (char d : s3) {
System.out.print(d);
}
System.out.println();
s2.addAll(s);
s2.addAll(s3);
System.out.println("没有被消除的字符是：");
for (char d : s) {
System.out.print(d);
}
}
}
3.使用Scanner从控制台读取一个字符串，统计字符串中每个字符出现的次数，要求使用学习过的知识完成以上要求
实现思路根据Set、List、Map集合的特性完成。
import java.util.ArrayList;import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Scanner;
import java.util.Set;
public class Test03 {
public static Scanner sc = new Scanner(System.in);
public static void main(String[] args) {
System.out.println("请输入一个字符串：");
String str = sc.next();
// 把字符串字符装入List集合
Map<Character,Integer> map = new HashMap<Character,Integer>();
char[] cs = str.toCharArray();
for (char c : cs) {
if (map.containsKey(c)) {
Integer value = map.get(c);
value++;
map.put(c, value);
}else{
map.put(c, 1);
}
}
//
Set<Character> set = map.keySet();
for (char c : set) {
System.out.println(c+"出现了"+map.get(c)+"次");
}
}
}
4.定义一个Employee类,属性:name:String,age:int,salary:double
把若干Employee对象放在List中,排序并遍历输出,排序规则:salary高的在前面,salary相同时age大的在前面,age也相同时按照name升序排列
把若干Employee对象放在Set中并遍历,要求没有重复元素
public class Employee {
public String name;
public int age;
public double salary;
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 getSalary() {
return salary;
}
public void setSalary(double salary) {
this.salary = salary;
}
public Employee() {
super();
// TODO Auto-generated constructor stub
}
public Employee(String name, int age, double salary) {
super();
this.name = name;
this.age = age;
this.salary = salary;
}
@Override
public String toString() {
return "姓名" + name + ", 年龄" + age + ", 工资" + salary ;
}
}
import java.util.ArrayList;
import java.util.List;
public class Test04 {
public static void main(String[] args) {
Employee e1 = new Employee("bob",20,5000);
Employee e2 = new Employee("jack",20,5000);
Employee e3 = new Employee("tom",21,5000);
Employee e4 = new Employee("lily",20,6000);
Employee e5 = new Employee("Mike",20,7000);
List<Employee> list = new ArrayList<Employee>();
list.add(e1);
list.add(e2);
list.add(e3);
list.add(e4);
list.add(e5);
//遍历
for (Employee e : list) {
System.out.println(e);
}
System.out.println("===============排序后===================");
for (int i = 1; i < list.size(); i++) {
for (int j = 0; j < list.size()-i; j++) {
Employee emp1 = list.get(j);
Employee emp2 = list.get(j+1);
//比较收入
if(emp1.getSalary() < emp2.getSalary()){
list.set(j, emp2);
list.set(j+1, emp1);
}else if(emp1.getSalary() == emp2.getSalary()){
if(emp1.getAge() < emp2.getAge()){
list.set(j, emp2);
list.set(j+1, emp1);
}
}else if(emp1.getAge() == emp2.getAge()){
if(emp1.getName().compareTo(emp2.getName())>0){
list.set(j, emp2);
list.set(j+1, emp1);
}
}
}
}
for (Employee e : list) {
System.out.println(e);
}
}
}