where is problem

有关任务的问题

包含猫的集

Java 语法, 第 8 级, 课程 11

已解决

实在没看出来哪里有问题🤣

1.在 Solution 类的内部，创建 public static Cat 类。
2.实现 createCats 方法。必须创建一个包含猫的 Set 并向其中添加 3 个猫。
3.在 main 方法中，从 Set cats 中删除一个猫。
4.实现 printCats 方法。该方法应显示集中剩余的所有猫。
每行显示一个猫。

要求：

程序应在屏幕上显示文本。
在 Solution 类的内部，必须包含一个具有默认构造方法的 public static Cat 类。
Solution 类的 createCats() 方法必须返回包含 3 个猫的 Set。
Solution 类的 printCats() 方法必须显示集中的所有猫。每行显示一个猫。
main() 方法应调用一次 createCats() 方法。
main() 方法应调用 printCats() 方法。
main() 方法必须从猫集中删除一个猫。

package zh.codegym.task.task08.task0819; import java.util.HashSet; import java.util.Set; /* 包含猫的集 */ public class Solution { public static void main(String[] args) { Set<Cat> cats = createCats(); //在此编写你的代码. 第 3 步 cats.remove(cats.toArray()[0]); printCats(cats); } public static Set<Cat> createCats() { //在此编写你的代码. 第 2 步 HashSet<Cat> cats = new HashSet<Cat>(); cats.add(new Cat("1")); cats.add(new Cat("2")); cats.add(new Cat("3")); return cats; } public static void printCats(Set<Cat> cats) { // 第 4 步 for(Cat cat : cats){ System.out.println(cat); } } // 第 1 步 public static class Cat{ String catName=""; public Cat(){ } public Cat(String name){ catName=name; } public String toString(){ return catName; } } }

受欢迎
新
旧

你必须先登录才能发表评论

Lisa L

级别 47 ，Nuremberg，Germany

5 五月 2022, 09:40

The print method looks good to may. So I guess validation has a problem somewhere else. Maybe it checks the references type you're trying to remove and gets confused somehow. If so then the task will fail cause toArray() returns an Object[] array and all elements are Objects. Just try yourself

System.out.println(cats.toArray()[0].catName);

won't work cause for a object reference the catName is unknown. You need a Cat reference to ouput the name. You could a) try to cast the element to a Cat or b) create a Cat[] array with using the overloaded toArray(T[] a) method...like

System.out.println(cats.toArray(new Cat[0])[0].catName);

If that doesn't do the trick I'd try to reset the task.

士兴彭

级别 15 ，Chongqing，China

9 五月 2022, 09:37

thank you for answer I try to used answer a,

for(Cat cat : cats){
      cats.remove(cat);
      break;
}

but it is wrong also

Lisa L

级别 47 ，Nuremberg，Germany

9 五月 2022, 11:32

有用的

try to remove lines 17-19... the task does not ask for that and a lot of task fail when it has additional output. and removing an element from a coillection in a for-each loop will not work. The for-each loop internally uses an iterator and when you use an iterator you only are allowed to use iterator methods to modify the collection. Means: for (Cat cat : cats) { you can not use to delete anything from the set But you could delete the element outside the loop

Cat toDel = null;
for(Cat cat : cats){
    toDel = cat;
    break;
}
cats.remove(toDel);

or you use the iterator

Iterator<Cat> it = cats.iterator();
if (it.hasNext()) {
    it.next();
    it.remove();
}

and as said, this may work as well but I do not know how CodeGym tests the code

Cat toDel =  cats.toArray(new Cat[0])[0];
cats.remove(toDel);

[this is for somewhen later: you could use streams to get a object from a collection]

cats.remove(cats.stream().findAny().get());

I'd use the second approach using an Iterator ;)

士兴彭

级别 15 ，Chongqing，China

10 五月 2022, 02:01

解决方法

Thank you for your suggestion; Unfortunately, the problem is not there🤣

when i delete these code, CodeGym allowed me through but i still not find where is problem😢