找不到符号方法Iterator（）

Question

Hello everyone i have started learning collection in java and trying to write a simple program but i am getting 2 errors please have a look and help me out.

import java.util.Iterator;
import java.util.*;
    class ArrayListDemo1{
    public static void main(String... s){
    ArrayList<Integer> al = new ArrayList<Integer>();
 // ArrayList al = new ArrayList();
    int x[] = {1, -1, 2, -2, 3, -3, 4, -4};
    for(int i=0; i<x.length;i++){
        al.add(x[i]);
    }
    System.out.println(al);
//  Iterator<Integer> i = al.Iterator();
    Iterator i = al.Iterator();
    while(i.hasNext()){
        Integer z = (Integer)i.next();
//      Integer z = i.next();
        if(z.intValue < 0)  
        i.remove(); 
    }   
    System.out.println(al);
}
}

Answer 1

 1. Iterator i = al.iterator();//here method is case sensitive
 2. intValue() not intValue, is a method.

Answer 2

Java is case sensitive and methods usually start in a lower case letter. It should be al.iterator();

Beside that, intValue is a method, so z.intValue should be z.intValue() .

Answer 3

1st Error

Methods usually follows camelcase and are case-sensitive.

It should be al.iterator()

Please have a look here

2nd Error

intValue() is a function, please refer this .

change if(z.intValue < 0) to if(z.intValue() < 0)

After Run, output

[1, -1, 2, -2, 3, -3, 4, -4]
[1, 2, 3, 4]

Tested here

Answer 4

并且您编写了intValue。它为false 。它应该为intValue（）。

Answer 5

You have 2 compile errors:

Iterator i = al.Iterator();

in java method names start with a lowercase character, also Iterator is a raw type, you should give it a generic type:

Iterator<Integer> i = al.iterator();

your second problem is here:

z.intValue

Integer doesn't have a public field intValue, but a method intValue() that returns the desired value:

z.intValue()

As a hint: I don't know why you use the Iterator here, but you could also use a for-each loop for the task of removing a list item:

for ( Integer integer : al )
{
    if ( integer.intValue() < 0 )
        al.remove( integer );
}