如何将一个 ArrayList 中的元素添加到另一个？

Question

So I have one ArrayList of fruits which has the name of the fruit and what its predominant vitamin is:

ArrayList<Foods> fruit; 
public Fruit() {
  fruit = new ArrayList<Foods>();
  fruit.add(new Foods("Orange", "Vitamin C"));
}

etc..

I want to add all the fruits with vitamin C to another array list so I iterated over them using:

Iterator vitC = fruit.iterator();
    while (vitC.hasNext()) {
        if (vitC.next().contains("Vitamin C")) {
            vitCfruit.add(vitC.next());
        }
}

However this adds the next value, so if apple was after orange in the list it would add apple to the next ArrayList instead of orange.

Answer 1

I'll ignore the apparent error in the code. In order to work with the element on the list you should do the following:

Iterator vitC = fruit.iterator();
    while (vitC.hasNext()) {
        Foods x = vitC.next();
        if (x.contains("Vitamin C")) { // should look for a Foods object here!!!
            administrators.add(x);
        }
}

Answer 2

the vitC.next() in the 'if' you declared will work, but you will not be accessing the same element in the next line when add it to the new list.

use a tmp variable to store the vitC.next() and in case it match the condition you can still add ot..

Iterator vitC = fruit.iterator();
    while (vitC.hasNext()) {
        tmp = vitC.next();
        if (tmp.contains("Vitamin C")) { // should look for a Foods object here!!!
            administrators.add(tmp);
        }
}

Answer 3

The enhanced for loop makes this straightforward:

for (Fruit thisFruit : fruit) {
    if (thisFruit.contains("Vitamin C")) {
        vitCfruit.add(thisFruit);
    }
}

In Java 8, this is simple with lambdas:

List<Foods> vitCfruit = fruit.stream()
    .filter(f -> f.contains("Vitamin C"))
    .collect(Collectors.toList());