这是代码
import java.util.EmptyStackException;
public class MyGenericStack<Item> implements MyGenericStackInterface<Item> {
private java.util.ArrayList<Item> list = new java.util.ArrayList<Item>();
/*
* Retrieve the item that was most recently added to the stack,
* which is the item at the top of the stack.
* The item is removed from the stack.
*/
public Item pop( ) throws EmptyStackException{
if (isEmpty()) throw new EmptyStackException();
else{
Item thing = null;
if(list.get(size()-1) == null){
thing = null;
}
else{
thing = list.get(size()-1);
}
return thing;
}
}
/*
* Retrieve the item at the top of the stack.
* Does not modify the stack.
*/
public Item peek( ) throws EmptyStackException{
if (isEmpty()) {
throw new EmptyStackException();
}
else{return list.get(size()-1);
}
};
/*
* Add item to the top of the stack.
*/
public void push( Item item ){
list.add(item);
};
/*
* Return true if the stack is empty
*/
public boolean isEmpty( ){
return list.isEmpty();
}
/*
* Return the number of items on the stack
*/
public int size( ){
return list.size();
};
}
问题是当我测试所有案例时，我得到了这8 个错误
java.lang.AssertionError: IsEmpty Error: isEmpty did not return true for empty stack after underflow.
java.lang.AssertionError: Peek Error: Peeking at null value on top of stack did not return null.
java.lang.AssertionError: Pop Error: Popping null value off stack did not return null.
java.lang.AssertionError: Push Error: Pushed multiple string values, but failed to retrieve them in order (via pop).
java.util.concurrent.TimeoutException (this test was labelled testReverseStringWithStack)
java.lang.AssertionError: Size Error: Size did not return correct size after pushes after underflow.
java.lang.AssertionError: Size Error: Size did not return 0 for empty stack after underflow.
java.lang.AssertionError: Push Error: Pushed multiple int values, but failed to retrieve them in order (via pop).
有什么办法可以解决这些问题吗？任何帮助表示赞赏。