如何从Java中的列表中删除当前元素

Question

How do I remove current element from list while iterating using for loop ?

I have below a list containing:

List<String> list = new ArrayList<String>();
        list.add("a");
        list.add("a2");
        list.add("a3");
        list.add("a4");
        list.add("a5");
        list.add("a6");
        list.add("a7");
        list.add("a8");
        list.add("a9");
        list.add("a10");
        list.add("a11");
        list.add("a12");
        list.add("a13");
        list.add("a14");
        list.add("a15");


        List<List<String>> parts = chopped(list, 4);
        System.out.println(parts);

which gives me output below like this:

[[a, a2, a3, a4], [a5, a6, a7, a8], [a9, a10, a11, a12], [a13, a14, a15]]

Now I am trying to remove first list from the list in below program:

for(int i=0; i<parts.size(); i++){

    System.out.println("Loop number: "+i);
    System.out.println("Current list: "+parts);         

    Thread.sleep(2000);
    parts.remove(i);

    System.out.println("After removing: "+parts);
}

Here I am using parts.remove(i); to remove current element, it gives me the following output:

[[a, a2, a3, a4], [a5, a6, a7, a8], [a9, a10, a11, a12], [a13, a14, a15]]
Loop number: 0
Current list: [[a, a2, a3, a4], [a5, a6, a7, a8], [a9, a10, a11, a12], [a13, a14, a15]]
After removing: [[a5, a6, a7, a8], [a9, a10, a11, a12], [a13, a14, a15]]
Loop number: 1
Current list: [[a5, a6, a7, a8], [a9, a10, a11, a12], [a13, a14, a15]]
After removing: [[a5, a6, a7, a8], [a13, a14, a15]]

This one removes first current element [a, a2, a3, a4] which is correct but in running second loop it removes [a9, a10, a11, a12] .

I want to remove it loop wise like below:

[[a, a2, a3, a4], [a5, a6, a7, a8], [a9, a10, a11, a12], [a13, a14, a15]]
[[a5, a6, a7, a8], [a9, a10, a11, a12], [a13, a14, a15]]
[[a9, a10, a11, a12], [a13, a14, a15]]
[[a13, a14, a15]]
[]

Edited:

When I try to access List inside List using parts.get(loopNumber) or parts.get(i)` it throws an exception error:

Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 2, Size: 1
    at java.util.ArrayList.rangeCheck(Unknown Source)
    at java.util.ArrayList.get(Unknown Source)
    at gmailSendLaptopGUI.MyProgram.main(MyProgram.java:156)

Answer 1

The problem is that you are editing the list and at the same time reading it.

You have to decrease the counter when you remove an object from the list.

for(int i=0; i<parts.size(); i++){

    System.out.println("Loop number: "+i);
    System.out.println("Current list: "+parts);         

    Thread.sleep(2000);
    parts.remove(i--);

    System.out.println("After removing: "+parts);
}

Answer 2

One more way to do is this:

 int loopNumber = 0;
    while (!parts.isEmpty()) {
        System.out.println("Loop" + loopNumber);
        parts.remove(0);
        loopNumber++;
        System.out.println(parts);
    }

Not sure why are you putting Thread.sleep().

Answer 3

You have already fine answers but I think that if you want to keep a for statement, a simple and readable way is not specifying increment ( i++ ) in the ForUpdate part of the for statement as it is not mandatory and you always want to suppress the current first element ( parts.remove(0) ).

for(int i=0; i<parts.size(); ){
   System.out.println("Current list: "+parts);         

   Thread.sleep(2000);
   parts.remove(0);

   System.out.println("After removing: "+parts);
}