execution of programms in java

Dear Sir Most of the examples in the handouts do not compile on the command prompt. just a few examples in the start are executed. I have correctly set the path also. in-spite when a run any code it gives many errors. for example in the following code is there any error. iport java.util.*; public class ArrayListTest { public static void main(String [] args){ ArrayList a1=new ArrayList(); Student s1=new Student ("ali", 1); Student s2=new Student ("Saad", 2); Student s3=new Student ("raza", 3); al.add(s2); al.add(s3); if (b==true){ System.out.println("arraylist size::" +size); } else{ int size=al.size(); System.out.println("arraylist size:" +size); } for (int i=0;i