你的位置:首页 > Java教程

[Java教程]集合练习


利用ArrayList

1、存储多个员工信息,包括工号,姓名,年龄,入职时间,逐条打印所有员工姓名,并输出员工个数。

package CollectionPart;import java.util.ArrayList;import java.util.List;public class ArrayListPractise_1 {    public static void main(String[] args) {        Employee_1 e1 = new Employee_1("dept1_001", "lifei", 24, "2016-03-28");    Employee_1 e2 = new Employee_1("dept1_002", "li2fe", 23, "2015-01-22");    Employee_1 e3 = new Employee_1("dept1_003", "lifei3", 28, "2016-02-05");    Employee_1 e4 = new Employee_1("dept2_001", "lif4i", 25, "2017-03-28");        List<Employee_1> myList1 = new ArrayList();    myList1.add(e1);    myList1.add(e2);    myList1.add(e3);    myList1.add(e4);        for (Employee_1 employee_1 : myList1) {      System.out.println(employee_1.getEmployeeName());    }    System.out.println("员工总个数为:"+myList1.size());      }}

package CollectionPart;public class Employee_1 {    private String employeeId;  private String employeeName;  private int employeeAge;  private String employeeHireDate;  /*  这里就存储成String 类型,在 数据库里面设置成 date格式。  然后 利用Date today = new Date();  SimpleDateFormat fm = new SimpleDateFormat("YYYY-MM-dd");  来做  */  public String getEmployeeId() {    return employeeId;  }  public void setEmployeeId(String employeeId) {    this.employeeId = employeeId;  }  public String getEmployeeName() {    return employeeName;  }  public void setEmployeeName(String employeeName) {    this.employeeName = employeeName;  }  public int getEmployeeAge() {    return employeeAge;  }  public void setEmployeeAge(int employeeAge) {    this.employeeAge = employeeAge;  }  public String getEmployeeHireDate() {    return employeeHireDate;  }  public void setEmployeeHireDate(String employeeHireDate) {    this.employeeHireDate = employeeHireDate;  }  @Override  public String toString() {    return "Employee_1 [employeeId=" + employeeId + ", employeeName=" + employeeName + ", employeeAge="        + employeeAge + ", employeeHireDate=" + employeeHireDate + "]";  }  public Employee_1(String employeeId, String employeeName, int employeeAge, String employeeHireDate) {    super();    this.employeeId = employeeId;    this.employeeName = employeeName;    this.employeeAge = employeeAge;    this.employeeHireDate = employeeHireDate;  }  public Employee_1() {    super();  }  }

 

练习2:

当有员工入职时添加,员工信息,当有员工离职时,删除该信息。

示例代码:【有bug,在 输入日期的时候,没等到输入日期,就直接询问是否还有入职的同志】

下面算是 为 解决 ConcurrentModificationException 提出了一个 方案。就是 得到 当前元素的 下标然后再删除。下面的代码没有怎么写注释,如果有问题的话欢迎讨论。

package CollectionPart;import java.util.ArrayList;import java.util.List;import java.util.Scanner;public class ArrayListPractise_2 {    public static void main(String[] args) {    ArrayListPractise_2 ap2 = new ArrayListPractise_2();        List<Employee_1> myList = new ArrayList();    System.out.println("是否有员工入职?");    Scanner in = new Scanner(System.in);    String string = in.nextLine();    while(string.equals("是")){      System.out.println("请输入员工的编号");      String id = in.nextLine();      System.out.println("请输入员工的姓名");      String name = in.nextLine();      System.out.println("请输入员工的年龄");      int age = in.nextInt();      System.out.println("请输入员工的入职时间");      String hireDate = in.nextLine();      System.out.println("?");      Employee_1 e1 = new Employee_1(id, name, age, hireDate);      myList.add(e1);      System.out.println("是否还有新员工入职?");      string = in.nextLine();    }            System.out.println("共有员工:"+myList.size()+"人");        List<Employee_1> newList =null;    System.out.println("是否有员工离职?");    string = in.nextLine();    while(string.equals("是")){      System.out.println("该员工的姓名是");      String name = in.nextLine();      newList = ap2.deleteFromTheList(myList,name);      System.out.println("是否还有员工离职?");      string = in.nextLine();    }    for (Employee_1 employee_1 : newList) {      System.out.println("员工人数为:"+newList.size());    }      }  private List<Employee_1> deleteFromTheList(List<Employee_1> myList, String name) {    int index = 0;    boolean hasTheElement = false;     for(int i = 0; i<myList.size();i++){      if(myList.get(i).getEmployeeName().equals(name)){        index = i;        hasTheElement = true;      }    }    if(!hasTheElement){      System.out.println("不存在此元素");    }else{      myList.remove(index);    }    return myList;  }}

ArrayList 和 LinkedList 分别在什么时候使用?

ArrayList,在遍历元素和随机访问元素时效率会比较高,在插入删除操作情况下效率会比较低

LinkedList,在插入和删除时效率会比较高,但是在 查找时效率会比较低