转载：https://beginnersbook.com/2013/12/how-to-initialize-an-arraylist/
Method 1: Initialization using Arrays.asList
Syntax:
ArrayList<Type> obj = new ArrayList<Type>(Arrays.asList(Object o1, Object o2, Object o3, ....so on));
Example:
import java.util.*;
public class InitializationExample1 {public static void main(String args[]) {ArrayList<String> obj = new ArrayList<String>(Arrays.asList("Pratap", "Peter", "Harsh"));System.out.println("Elements are:"+obj);}
}
Output:
Elements are:[Pratap, Peter, Harsh]
Method 2: Anonymous inner class method to initialize ArrayList
Syntax:
ArrayList<T> obj = new ArrayList<T>(){{add(Object o1);add(Object o2);add(Object o3);......}};
Example:
import java.util.*;
public class InitializationExample2 {public static void main(String args[]) {ArrayList<String> cities = new ArrayList<String>(){{add("Delhi");add("Agra");add("Chennai");}};System.out.println("Content of Array list cities:"+cities);}
}
Output:
Content of Array list cities:[Delhi, Agra, Chennai]
Method3: Normal way of ArrayList initialization
Syntax:
ArrayList<T> obj = new ArrayList<T>();obj.add("Object o1");obj.add("Object o2");obj.add("Object o3");......
Example:
import java.util.*;public class Details {public static void main(String args[]) {ArrayList<String> books = new ArrayList<String>();books.add("Java Book1");books.add("Java Book2");books.add("Java Book3");System.out.println("Books stored in array list are: "+books);}
}
Output:
Books stored in array list are: [Java Book1, Java Book2, Java Book3]
Method 4: Use Collections.ncopies
Collections.ncopies method can be used when we need to initialize the ArrayList with the same value for all of its elements. Syntax: count is number of elements and element is the item value
ArrayList<T> obj = new ArrayList<T>(Collections.nCopies(count, element));
Example:
import java.util.*;public class Details {public static void main(String args[]) {ArrayList<Integer> intlist = new ArrayList<Integer>(Collections.nCopies(10, 5));System.out.println("ArrayList items: "+intlist);}
}
Output:
ArrayList items: [5, 5, 5, 5, 5, 5, 5, 5, 5, 5]
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