Size
ArrayList don't need a size.
/**
* ArrayList class is a resizable array,
* ArrayList don't need an index and are parameterized.
*/
package com.minte9.collections.lists;
import java.util.ArrayList;
public class Size {
public static void main(String[] args) {
String[] myList = new String[2]; // Corect, with dimension
System.out.println(myList.length); // 2
// myList = new String[]; // Error: must provide dimension
ArrayList<String> myArrayList;
myArrayList = new ArrayList<>(); // no dimension needed
System.out.println(myArrayList.size()); // 0
myArrayList.add("a");
System.out.println(myArrayList.size()); // 1
System.out.println(myArrayList.contains("a")); // true
ArrayList<Button> myButtons = new ArrayList<>(); // parameterized
myButtons.add(new Button());
System.out.println(myButtons.size()); // 1
}
}
class Button {
}
Loop
You can loop through an ArrayList with the enhanced for.
/**
* ArrayList can be parsed easily with enhanced for.
*
* ArrayDeque can add elements to the head as fast as to the tail.
* If you are modifing the tail only, the ArrayList is a preferred.
*/
package com.minte9.collections.lists;
import java.util.ArrayDeque;
import java.util.ArrayList;
public class Loop {
public static void main(String[] args) {
ArrayList<String> myList = new ArrayList<String>();
myList.add("a");
myList.add("b");
myList.add(0, "c"); // add to first position
for(String v:myList) {
System.out.println(v); // c a b
}
ArrayDeque<Integer> myDeque = new ArrayDeque<>();
myDeque.addFirst(1);
myDeque.add(2);
myDeque.addLast(10);
myDeque.forEach(System.out::println); // 1 2 10
}
}
Last update: 595 days ago
