[实验任务一]：多次撤销
改进课堂上的“用户信息操作撤销”实例，使得系统可以实现多次撤销（可以使用HashMap、ArrayList等集合数据结构实现）。
实验要求：
1. 提交源代码；
package rjsj.no20;
public class Client {
public static void main(String[] args) {
User user = new User();
Caretaker caretaker = new Caretaker();
user.setId("20193288");
user.setPassword("123456");
caretaker.setMemo(user.saveState());
System.out.println("״̬һ");
user.show();
System.out.println("************************************************************");
user.setId("20193288");
user.setPassword("qwerasdfzxcv");
caretaker.setMemo(user.saveState());
System.out.println("״̬¶þ");
user.show();
System.out.println("************************************************************");
user.setId("20183288");
user.setPassword("66666666");
caretaker.setMemo(user.saveState());
System.out.println("״̬Ƚ");
user.show();
System.out.println("************************************************************");
System.out.println("ְ²½³·Ϻ²ٗ÷£º");
System.out.println("»ָ´µ½״̬¶þ");
user.restoreState(caretaker.getMemo());
user.show();
System.out.println("************************************************************");
System.out.println("»ָ´µ½״̬һ");
user.restoreState(caretaker.getMemo());
user.show();
}
}
package rjsj.no20;
public class Memo {
private String id;
private String password;
public Memo(String id, String password) {
this.id = id;
this.password = password;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
}
package rjsj.no20;
public class User {
private String id;
private String password;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public Memo saveState(){
return new Memo(id,password);
}
public void restoreState(Memo m){
this.id = m.getId();
this.password = m.getPassword();
}
public void show(){
System.out.println("id:" + this.id);
System.out.println("password:" + this.password);
}
}
package rjsj.no20;
import java.util.ArrayList;
import java.util.List;
public class Caretaker {
private List<Memo> list = new ArrayList<>();
public void setMemo(Memo m){
list.add(m);
}
public Memo getMemo(){
Memo m = list.get( list.size() - 2 );
list.remove( list.size() - 2 );
return m;
}
}
2. 注意编程规范。