/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
	    List<String> al = appendOne(new ArrayList<>(), "1");
	    List<String> bl = appendOne(al, "2");
	    System.out.println(bl); 
	}
 
	private static <T> List<T> appendOne(List<T> al, T t) {
	    List<T> bl = new ArrayList<>(al);
	    bl.add(t);
	    return Collections.unmodifiableList(bl);
	}
}

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