首先我会告诉你我的问题是什么,下面是代码:
当我运行Class1
时,我可以注册第一个对象,该对象会获得唯一ID。之后,我注册了第二个对象,该对象也有唯一的ID。然后我尝试通过询问第一个对象的ID来检索我的第一个对象信息。现在的问题是,当我要求添加到ArrayList
的第一个对象时,将始终打印出以下内容:“ID错误。您无法检索对象信息。” 然而,当我尝试检索我的第二个对象(最后添加到ArrayList
的对象)时,它会打印出就像我想要的那样。< / p>
我的问题是,为什么我只能访问添加到ArrayList
的最后一个对象,如何使用其唯一ID打印第一个对象信息?
这是Class1
:
import java.util.Scanner;
import java.util.*;
public class Class1 {
public static void main(String[] args){
Class1 class1 = new Class1();
class1.presentoptions();
class1.createObject();
}
Scanner sc = new Scanner(System.in);
String name;
String ID;
double salary;
Class2 class2;
final String END_LINE = System.lineSeparator();
public void presentoptions(){
class2 = new Class2();
while (true){
System.out.println("=== Welcome === ");
System.out.println("Choose an option below: ");
System.out.println(" ");
System.out.println("1. Register an object. ");
System.out.println("2. Retrieve an objects information. ");
System.out.println("3. Quit this program. ");
int option = sc.nextInt();
switch (option) {
case 1:
System.out.println("What type of object? " + END_LINE
+ " - Worker. " + END_LINE);
// other objects
String type = sc.nextLine();
createObject(); // creating the specified employee
break;
case 2:
class2.retrieveObject();
break;
case 3:
System.out.println("You've quitted the program.");
System.exit(0);
default:
System.out.println("Error. Please try again.");
break;
}
}
}
public void createObject(){
class2 = new Class2();
System.out.println("Write the name of the object (worker): ");
String typeofobject = sc.nextLine();
UUID uniqueID = UUID.randomUUID();
String x = "" + uniqueID;
System.out.println("The new ID of the " + typeofobject + " is: " + uniqueID + ".");
System.out.println();
System.out.println("What's the name of the new " + typeofobject + "?");
name = sc.nextLine();
System.out.println("What's the salary of the new " + typeofobject + "?");
salary = sc.nextDouble();
Employee employee = new Employee(x, name, salary);
switch (typeofobject) {
case "Worker":
class2.registerObject(employee);
break;
default:
System.out.println("You missspelled the type of object. Run the program again.");
break;
}
}
}
这是Class2
:
import java.util.Scanner;
import java.util.ArrayList;
class Class2 extends Class1{
Scanner input = new Scanner(System.in);
ArrayList<Employee> employees = new ArrayList<Employee>();
final String END_OF_LINE = System.lineSeparator();
public void registerObject(Employee employee){
employees.add(employee);
}
public void retrieveObject() {
System.out.println("Which objects information do you want to retrieve? Type in his/her ID.");
String inputNewID = input.nextLine();
for(Employee employee: employees){
if(inputNewID.equals(employee.getID())){
System.out.println("ID: " + employee.ID + END_OF_LINE + "Name: " + employee.name + END_OF_LINE + "Salary: " + employee.grossSalary);
} else {
System.out.println("The ID is wrong. You can't retrieve the objects information.");
}
}
}
}
最后,Employee
类:
import java.util.*;
public class Employee {
protected String ID;
protected String name;
protected double grossSalary;
final String END_OF_LINE = System.lineSeparator();
public String getID() {
return ID;
}
public Employee (String ID, String name, double grossSalary){
this.ID = ID;
this.name = name;
this.grossSalary = grossSalary;
}
}
感谢。
答案 0 :(得分:1)
你有一行
OK
1
Time taken: 0.912 seconds, Fetched: 1 row(s)
在您的class2 = new Class2();
方法中。但createObject()
是您拥有员工ArrayList的地方。因此,每当您致电class2
时,您只是在吹走旧的ArrayList。
我认为你可以摆脱那条线。
答案 1 :(得分:0)
注意for循环:
for(Employee employee: employees){
if(inputNewID.equals(employee.getID())){
System.out.println("ID: " + employee.ID + END_OF_LINE + "Name: " + employee.name + END_OF_LINE + "Salary: " + employee.grossSalary);
} else {
System.out.println("The ID is wrong. You can't retrieve the objects information.");
}
}
它将在员工列表中打印FOR EACH对象,无论它是否与inputNewID相等,我认为其意图是在ONCE中打印。
你可以使用布尔标志获得想要的行为:
boolean isEmployeeFound = false;
for(Employee employee: employees){
if(inputNewID.equals(employee.getID())){
isEmployeeFound = true;
System.out.println("ID: " + employee.ID + END_OF_LINE + "Name:"+employee.name + END_OF_LINE + "Salary: " + employee.grossSalary);
}
}
if(!isEmployeeFound){System.out.println("The ID is wrong. You can't retrieve the objects information.");}
另外正如其他提到的那样摆脱了createObject函数中的class2 = new Class2()行。
答案 2 :(得分:0)
问题在于Class2的for循环中的if / else,或者更具体地说是else。在循环的第一个元素上,将触发else以给出消息。处理这个问题的一种方法是添加一个布尔值来检查是否找到了ID,并在循环之后将else块更改为if检查:
boolean idFound = false;
for(Employee employee: employees){
if(inputNewID.equals(employee.getID())){
idFound = true;
System.out.println("ID: " + employee.ID + END_OF_LINE + "Name: " + employee.name + END_OF_LINE + "Salary: " + employee.grossSalary);
}
}
if(! idFound) {
System.out.println("The ID: " + inputNewID + " is not found. You can't retrieve the objects information.");
}