idea中java使用集合进行简单的增删改查

package com.java.dao;

import com.java.model.User;

public interface UserDao {
//1.初始化数据
void doInitUser();
//2.新增用户
boolean doAddUser(User user);

//3.删除用户
boolean doDelUser(int uid);

//4.修改用户
boolean doModUser(int uid);

//5.通过id查询用户
User doFindById(int uid);

//6.回显所有的信息
void doPringAll();

}
package com.java.dao.impl;

import com.java.dao.UserDao;
import com.java.model.User;
import com.java.util.UserUtil;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class UserDaoImpl implements UserDao {

List<User> uList=new ArrayList<>();   //泛型和多态体现
// 不知道List里面装什么的时候用Object


@Override
public void doInitUser() {
    User u1=new User(1001,"admin","admin");
    User u2=new User(1002,"root","123456");
    uList.add(u1);
    uList.add(u2);
}

/*
/@param user是通过UserUtil获取
@return true新增成功，false新增失败
 */
@Override
public boolean doAddUser(User user) {
    try {
        uList.add(user);
        System.out.println("新增成功！");
        return true;
    }catch (Exception e){
        return false;
    }

}

@Override
public boolean doDelUser(int uid) {
    try {
        //取每个元素操作
        Iterator it=uList.iterator();   //取出容器中所有的元素
        while (it.hasNext()){   //判断容器中是否存在元素,相当于数组的判空操作
            User user = (User) it.next();   //取出元素

            if (user.getUid()==uid){        //找到了需要删除的uid
                uList.remove(user);
                System.out.println("删除成功！");
            }

        }
        return true;
    }catch (Exception e){
        return false;
    }

}

@Override
public boolean doModUser(int uid) {
    try {
        Iterator it=uList.iterator();
        while (it.hasNext()){
            User user= (User) it.next();
            if (user.getUid()==uid){
                User modUser=new UserUtil().getUser("修改后");

                //设置 计算机事别ITERATOR认为你取出来的是Object，并不是一个User，所以计算机看不懂你到底要修改什么
                user.setUid(modUser.getUid());
                user.setUsername(modUser.getUsername());
                user.setPassword(modUser.getPassword());
                System.out.println("修改成功！");
            }
        }
        return true;
    }catch (Exception e){
        return false;
    }

}

@Override
public User doFindById(int uid) {
    User user=null;
    try {
        Iterator it=uList.iterator();
        while (it.hasNext()){
            user= (User) it.next();
            if (user.getUid()==uid){
                return user;
            }
        }

        return user;
    }catch (Exception e){
        return user;
    }

}

@Override
public void doPringAll() {
    //高级for循环 - 遍历
    for (User u:uList){
        if (u!=null){
            System.out.println(u);
        }
    }
}

public static void main(String[] args) {
    UserDao dao=new UserDaoImpl();  //接口是不能直接new的
    dao.doInitUser();
    dao.doPringAll();

    User user=new UserUtil().getUser("新增");
    dao.doAddUser(user);
    dao.doPringAll();

    int uid=new UserUtil().getUid("修改");
    dao.doModUser(uid);
    dao.doPringAll();
}

}
package com.java.service;

import com.java.model.User;

public interface UserService {
//1.初始化数据
void doInitUser();
//2.新增用户
boolean doAddUser(User user);

//3.删除用户
boolean doDelUser(int uid);

//4.修改用户
boolean doModUser(int uid);

//5.通过id查询用户
User doFindById(int uid);

//6.回显所有的信息
void doPringAll();

}
package com.java.service.impl;

import com.java.dao.UserDao;
import com.java.dao.impl.UserDaoImpl;
import com.java.model.User;
import com.java.service.UserService;

public class UserServiceImpl implements UserService {

UserDao dao=new UserDaoImpl();

@Override
public void doInitUser() {
    dao.doInitUser();

}

@Override
public boolean doAddUser(User user) {
    boolean b= dao.doAddUser(user);
    if (b){
        System.out.println("新增成功！");
        return true;
    }else{
        System.out.println("新增失败！");
        return false;
    }
}

@Override
public boolean doDelUser(int uid) {
    boolean b=dao.doDelUser(uid);
    if (b){
        System.out.println("删除成功！");
        return true;
    }else{
        System.out.println("删除失败！");
        return false;
    }
}

@Override
public boolean doModUser(int uid) {
    boolean b=dao.doDelUser(uid);
    if (b){
        System.out.println("修改成功！");
        return true;
    }else{
        System.out.println("修改失败！");
        return false;
    }
}

@Override
public User doFindById(int uid) {
    return dao.doFindById(uid);
}

@Override
public void doPringAll() {
    dao.doPringAll();
}

}
package com.java.util;

import com.java.model.User;

import java.util.Scanner;

public class UserUtil {

Scanner in=new Scanner(System.in);
//1.获取User对象
public User getUser(String str){
    System.out.println("请您输入需要"+str+"的用户编号：");
    int uid=in.nextInt();
    System.out.println("请您输入需要"+str+"的用户名称：");
    String username=in.next();
    System.out.println("请您输入需要"+str+"的用户密码：");
    String password=in.next();

    User user=new User(uid,username,password);
    return user;
};

//2.获取需要操作的uid
public int getUid(String str){
    System.out.println("请您输入需要"+str+"的用户编号：");
    int uid=in.nextInt();
    return uid;
}

}