Amazing JAVA: Learn JAVA Quickly! by Andrei Besedin

Author:Andrei Besedin [Besedin, Andrei]
Language: eng
Format: epub
Published: 2017-06-23T07:00:00+00:00

ArrayList represents dynamic Collection. Methods for manipulating elements are:

add() – for adding element to ArrayList

remove() – for removing elements from ArrayList

get() – for getting elements from ArrayList

It is time to see some example of ArrayList. So, let`s create a new package third.pack and class Array inside.

ArrayList<Integer>ar = new ArrayList<Integer>();

ar.add(1);

ar.add(2);

ar.add(3);

System.out.println("Size of ArrayList is: " + ar.size());

ar.remove(0);

intnum = ar.get(0);

System.out.println(num);

System.out.println("New size of ArrayList is: " + ar.size());

expected: Size of ArrayList is: 3 will be printed to console

2

New size of ArrayList is: 2

So, in our code is used everything that is mentioned about ArrayList. First it is declared. We said that arrays have one big disadvantage, they are not supposed to change they size. But as you can see, our ArrayList is dynamic, three elements are added(Size of ArrayList is: 3). Compiler count elements from 0, so 1 = 0, 2 = 1, 3 = 2. It is important to remember that because of manipulation of elements. Another operation is removing first element from our array. Variable num holds, by get(0) method, first element and println print it to console(2). Also, size is not anymore 3, it I s now 2.

What if we have bigger ArrayList and we want to print all values? For loop is solution, of course:

for (intcounter = 0; counter<ar.size(); counter++) {

System.out.println(ar.get(counter));

}//for loop

for (Integer n : ar) {

System.out.println(n);

}//for each loop, same result

HashMap

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