3-8作业问题
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 | package com.Imooc;public class Department { private int departmentid; private String departmentname; private Staff[] myStaff; private int staffNum;public Department(){ }public Department(int departmentid,String departmentname){ this.departmentid =departmentid; this.departmentname =departmentname; }public int getDepartmentid() { return departmentid;}public String getDepartmentname() { return departmentname;}public void setDepartmentid(int departmentid) { this.departmentid = departmentid;}public void setDepartmentname(String departmentname) { this.departmentname = departmentname;}public Staff[] getMyStaff() { if(this.myStaff==null) this.myStaff =new Staff[20]; return myStaff;}public int getStaffNum() { return staffNum;}public void setMyStaff(Staff[] myStaff) { this.myStaff = myStaff;}public void setPostNu(int staffNum) { this.staffNum = staffNum;}public void addStaff(Staff sta){ for(int i=0;i<this.getMyStaff().length;i++){ if(this.getMyStaff()[i]==null){ this.getMyStaff()[i]=sta; this.staffNum=i+1; return; } }} } |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 | package com.Imooc;public class Staff {//成员属性：员工姓名，工号，年龄，性别，所属部门，职务信息private String staffname;private String staffid;private int staffage;private String staffsex;private Department staffdepartment;private Post staffpost;//无参构造方法public Staff(){ }//带参构造方法，实现对属性的全部赋值public Staff(String staffname,String staffid,int staffage,String staffsex){ this.staffname=staffname; this.staffid =staffid; this.setStaffage(staffage); this.setStaffsex(staffsex); }public String getStaffname() { return staffname;}public String getStaffid() { return staffid;}public int getStaffage() { return staffage;}public String getStaffsex() { return staffsex;}public Department getStaffdepartment() { return staffdepartment;}public Post getStaffpost() { return staffpost;}public void setStaffname(String staffname) { this.staffname = staffname;}public void setStaffid(String staffid) { this.staffid = staffid;}//设置年龄限制，必须在18-65之间，否则强制默认为18public void setStaffage(int staffage) { if(staffage>=18&&staffage<=65){ this.staffage = staffage; } else{ this.staffage=18; } }//设定性别只能是“男”或“女”，反之则设置默认为“男”public void setStaffsex(String staffsex) { if(staffsex.equals("女")){ this.staffsex = staffsex; } else{ this.staffsex = "男"; }}public void setStaffdepartment(Department staffdepartment) { this.staffdepartment = staffdepartment;}public void setStaffpost(Post staffpost) { this.staffpost = staffpost;}public String info(Department staffdepartment, Post staffpost){ String str="姓名:"+this.getStaffname()+"\n工号"+this.getStaffid()+"\n年龄"+this.getStaffage()+"\n性别"+this.getStaffsex()+"\n职务:"+this.getStaffdepartment().getDepartmentname()+this.getStaffpost().getPostname(); return str; }} |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 | package com.Imooc;public class Post {private int postid;private String postname;public Post(){ }public Post(int postid,String postname){this.postid=postid;this.postname=postname;}public int getPostid() { return postid;}public String getPostname() { return postname;}public void setPostid(int postid) { this.postid = postid;}public void setPostname(String postname) { this.postname = postname;}} |
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 | package com.Imooc;public class Test { public static void main(String[] args) { // TODO Auto-generated method stubDepartment dep1=new Department(1,"人事部");Department dep2=new Department(2,"市场部");Post po1=new Post(1,"经理");Post po2=new Post(2,"助理");Post po3=new Post(3,"职员");Staff sta1=new Staff("张铭","S001",29,"男");Staff sta2=new Staff("李艾爱","S002",21,"女");Staff sta3=new Staff("孙超","S004",29,"男");Staff sta4=new Staff("张美美","S005",26,"女");Staff sta5=new Staff("蓝迪","S006",37,"男");Staff sta6=new Staff("米莉","S007",24,"女");dep1.addStaff(sta1);dep1.addStaff(sta2);dep1.addStaff(sta3);dep2.addStaff(sta4);dep2.addStaff(sta5);dep2.addStaff(sta6);System.out.println(sta1.info(dep1,po1));System.out.println("=================================");System.out.println(sta1.info(dep1,po2));System.out.println("=================================");System.out.println(sta1.info(dep1,po3));System.out.println("=================================");System.out.println(sta1.info(dep2,po3));System.out.println("=================================");System.out.println(sta1.info(dep2,po1));System.out.println("=================================");System.out.println(sta1.info(dep2,po3));System.out.println("=================================");System.out.println("人事部总共有"+dep1.getStaffNum()+"名员工");System.out.println("市场部总共有"+dep2.getStaffNum()+"名员工"); }} |
1 2 3 | Exception in thread "main" java.lang.NullPointerException at com.Imooc.Staff.info(Staff.java:75) at com.Imooc.Test.main(Test.java:24) |
为什么会出现空指针错误，哪里出错了？该改成什么样？
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因为你Staff类的初始化并没有给对应的Department和Post赋值，而info()方法中你传递了部门和职务对象，但是获取值的时候部门和职务是通过Staff员工类中的部门和职务熟悉的get方法获取的，但是并没有set，所以无法获取这两个属性的值。两种修改方法都可以：
1、在Staff类中的info()方法中，直接通过staffdepartment和staffpost两个参数对象调用对应的get方法获取名称即可。
2、在Staff类中将构造方法的参数在加入部门和职务对象参数，然后在Test类中初始化员工对象的时候，可以将对应的部门和职务对象传递进去即可。
上述方式可以选择一种进行修改。
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