下面代码哪一行有编译错误

public class Outer {
    public static int a;
    private int b;
    public static class Inner{
        public void print(){
            System.out.println(a);
            System.out.println(b);
        }
    }
}

1. public static int a;
2. public static class Inner
3. System.out.println(a);
4. System.out.println(b);