堆栈泛型类工作不

Question

可能重复：
Java how to: Generic Array creation

import java.util.EmptyStackException; 
import java.util.Vector; 

public class Stack<E> extends Vector<E> { 
    private E a[]; 
    private int top; 

    public void Stack() { 
     a = new E[100]; 
     top = -1; 
    } 

    public void Stack(int n) { 
     a = new E[n]; 
     top = -1; 
    } 

    public E pop() { 
     E obj; 
     int len = size(); 
     if (top == -1) 
      throw new EmptyStackException(); 
     else 
      obj = a[top--]; 
     return obj; 
    } 

    public void push(E e) { 
     if (e == null) 
      throw new NullPointerException(); 
     else if (top == size() - 1) 
      System.out.println("Stack full"); 
     else { 
      a[++top] = e; 
      System.out.println("pushed :" + e); 
     } 

    } 

    public int size() { 
     int i; 
     for (i = 0; a[i] != null; i++) 
      ; 
     return i; 
    } 

} 

这是我的筹码仿制药Java类。我在两个构造函数（即Stack（）和Stack（int n））中获得数组声明中的错误。在这两种情况下，错误都是“通用数组创建”。请帮助

Answer 1

通用数组无法创建。所以使用Object数组。

import java.io.*; 
import java.util.EmptyStackException; 
import java.util.Vector; 
public class Stack extends Vector 
{ 
    private Object a[]; 
    private int top; 
    public void Stack() 
    { 
    a=new Object[100]; 
    top=-1; 
    } 
    public void Stack(int n) 
    { 
    a=new Object[n]; 
    top=-1; 
    } 
    public E pop() 
    { 
    E obj; 
    int len = size(); 
    if (top == -1) 
     throw new EmptyStackException(); 
    else 
     obj=(E) a[top--]; 
    return obj; 
    } 
    public void push(E e) 
    { 
    if(e==null) 
     throw new NullPointerException(); 
    else if(top==size()-1) 
     System.out.println("Stack full"); 
    else 
    { 
     a[++top]=e; 
     System.out.println("pushed :"+e); 
    } 


} 
public int size() 
{ 
    int i; 
    for(i=0;a[i]!=null;i++); 
    return i; 
} 
} 

Answer 2

你的类没有构造函数，这些都是方法。为construtors删除void类型。构造函数没有返回类型。此外，您的班级名称以低字母堆栈开始，构造函数以堆栈开始。将你的类重命名为Stack并删除void类型。

你需要做的是这样的

 public Stack(Class<E> cls) 
{ 
     a = (E[]) Array.newInstance(cls); 

    top=-1; 
} 

public Stack(Class<E> cls,int n) 
    { 
    a = (E[]) Array.newInstance(cls,n); 
    top=-1; 
    } 

看到Generic Array

以下是在main方法创建对象的工人阶级。

class Stack<E> extends Vector<E> { 
    private E a[]; 
    private int top; 

    public Stack(Class<E> cls) 
    { 


     a = (E[]) Array.newInstance(cls); 

     top=-1; 
    } 

    public Stack(Class<E> cls,int n) 
    { 


     a = (E[]) Array.newInstance(cls,n); 

     top=-1; 
    } 

    public E pop() { 
     E obj; 
     int len = size(); 
     if (top == -1) 
      throw new EmptyStackException(); 
     else 
      obj = a[top--]; 
     return obj; 
    } 

    public void push(E e) { 
     if (e == null) 
      throw new NullPointerException(); 
     else if (top == size() - 1) 
      System.out.println("Stack full"); 
     else { 
      a[++top] = e; 
      System.out.println("pushed :" + e); 
     } 

    } 

    public int size() { 
     int i; 
     for (i = 0; a[i] != null; i++) 
      ; 
     return i; 
    } 

    public static void main(String...strings){ 
     Stack<Integer> st=new Stack<Integer>(Integer.class,n); 
    } 

}