public GenericTest1(Object a)
        ...{
            this.a = a;
        }

        public Object getA() ...{
            return a;
        }

        public void setA(Object a) ...{
            this.a = a;
        }

        public static void main(String[] args)
        ...{
            GenericTest1 g1 = new GenericTest1("1");
            String str = (String)g1.getA();          ①
            g1.setA(1);　　　　　　　　　　　　  ②
            Integer x = (Integer) g1.getA();
        }
    }

    public class GenericTest2 <T> ...{
        private T a;

        public GenericTest2(T a)
        ...{
            this.a = a;
        }

        public T getA() ...{
            return a;
        }

        public void setA(T a) ...{
            this.a = a;
        }

        public static void main(String[] args)
        ...{
            GenericTest2<String> g2 = new GenericTest2<String>("1");
            String str = g2.getA();                  ①
            // 编译时错误
            g2.setA(1)；                                           ②
        }
    }

    public class GenericTest3 implements GenericInterface<Integer> ...{
        private int[] a;
        private int size;
        private int pos = 0;
        private int addPos = 0;

        public GenericTest3(int sz)
        ...{
            this.size = sz;
            a = new int[sz];
        }

        public Integer next()
        ...{
            if ( pos > addPos - 1 )
            ...{
                pos = 0;
            }

            return a[pos++];
        }

        public boolean hasNext()
        ...{
            return !(pos == addPos);
        }

        public boolean add(int value)
        ...{
            if ( addPos >= size )
            ...{
                return false;
            }
            else
            ...{
                a[addPos++] = value;
                return true;
            }
        }

        public int getSize() ...{
            return size;
        }
    }

    public class GenericTest4 implements GenericInterface<String> ...{
        private String[] a;
        private int size;
        private int pos = 0;
        private int addPos = 0;

        public GenericTest4(int sz)
        ...{
            this.size = sz;
            a = new String[sz];
        }

        public String next()
        ...{
            if ( pos > addPos - 1 )
            ...{
                pos = 0;
            }

            return a[pos++];
        }

        public boolean hasNext()
        ...{
            return !(pos == addPos);
        }

        public boolean add(String value)
        ...{
            if ( addPos >= size )
            ...{
                return false;
            }
            else
            ...{
                a[addPos++] = value;
                return true;
            }
        }

        public int getSize() ...{
            return size;
        }
    }

    public class GenericTest5 ...{
        public static void main(String[] args)
        ...{
            GenericTest3 g3 = new GenericTest3(3);
            GenericTest4 g4 = new GenericTest4(4);
            String[] values = "a,b,c,d,e,f,g,h,i,j,k,l".splIT(",");

            for (int i = 0; i < g3.getSize(); i++)
            ...{
                g3.add(i);
            }

            for (int i = 0; i < g4.getSize(); i++)
            ...{
                g4.add(values[i]);
            }

            while(g3.hasNext())
            ...{
                System.out.println(g3.next());
            }

            while(g4.hasNext())
            ...{
                System.out.println(g4.next());
            }
        }
    }