Strings and StringBuffer Project

So, I've been working on a school project for a couple days, and I have my code written out but I can't fix the compile-time errors.

The prompt for it is here:

Write two programs: one using the String class and one using the StringBuffer class. Your programs should store a set of Strings in an ArrayList and print those Strings in the order by which they are added. The output of your programs should create a complete sentence.

I am stuck on the first program.

Here's my code for the first program:

Java Code:

import java.util.ArrayList;

public class SentenceNormal {
        public static void main(String args[]) {
                String n1 = "My ";
                String n2 = "favorite ";
                String n3 = "football ";
                String n4 = "team ";
                String n5 = "is ";
                String n6 = "the ";
                String n7 = "Seahawks";
                ArrayList sentence = new ArrayList();
                sentence.add(0,n1);
                sentence.add(1,n2);
                sentence.add(2,n3);
                sentence.add(3,n4);
                sentence.add(4,n5);
                sentence.add(5,n6);
                sentence.add(6,n7);
                for (int i=0; i<7; i++) {
                        System.out.print(sentence.get(i));
                }
                System.out.print(".");
        }
}

The first error I get says this:

C:\Users\Lauren\Dropbox\Schoolwork\9th Grade\Java Programming\Unit 4 - Strings\U

nit Project>javac SentenceNormal.java

Note: SentenceNormal.java uses unchecked or unsafe operations.

Note: Recompile with -Xlint:unchecked for details.

After I add the "-Xlint" I get this:

C:\Users\Lauren\Dropbox\Schoolwork\9th Grade\Java Programming\Unit 4 - Strings\U

nit Project>javac -Xlint SentenceNormal.java

SentenceNormal.java:12: warning: [rawtypes] found raw type: ArrayList

ArrayList sentence = new ArrayList();

^

missing type arguments for generic class ArrayList<E>

where E is a type-variable:

E extends Object declared in class ArrayList

SentenceNormal.java:12: warning: [rawtypes] found raw type: ArrayList

ArrayList sentence = new ArrayList();

^

missing type arguments for generic class ArrayList<E>

where E is a type-variable:

E extends Object declared in class ArrayList

SentenceNormal.java:13: warning: [unchecked] unchecked call to add(int,E) as a m

ember of the raw type ArrayList

sentence.add(0,n1);

^

where E is a type-variable:

E extends Object declared in class ArrayList

SentenceNormal.java:14: warning: [unchecked] unchecked call to add(int,E) as a m

ember of the raw type ArrayList

sentence.add(1,n2);

^

where E is a type-variable:

E extends Object declared in class ArrayList

SentenceNormal.java:15: warning: [unchecked] unchecked call to add(int,E) as a m

ember of the raw type ArrayList

sentence.add(2,n3);

^

where E is a type-variable:

E extends Object declared in class ArrayList

SentenceNormal.java:16: warning: [unchecked] unchecked call to add(int,E) as a m

ember of the raw type ArrayList

sentence.add(3,n4);

^

where E is a type-variable:

E extends Object declared in class ArrayList

SentenceNormal.java:17: warning: [unchecked] unchecked call to add(int,E) as a m

ember of the raw type ArrayList

sentence.add(4,n5);

^

where E is a type-variable:

E extends Object declared in class ArrayList

SentenceNormal.java:18: warning: [unchecked] unchecked call to add(int,E) as a m

ember of the raw type ArrayList

sentence.add(5,n6);

^

where E is a type-variable:

E extends Object declared in class ArrayList

SentenceNormal.java:19: warning: [unchecked] unchecked call to add(int,E) as a m

ember of the raw type ArrayList

sentence.add(6,n7);

^

where E is a type-variable:

E extends Object declared in class ArrayList

9 warnings

I honestly have no clue what to do, as my syntax looks right to me. I am still semi-new to Java so I have no idea what is wrong with my code.

Anyone help?