泛型：所谓泛型，就是变量的类型参数化。

作用：限制泛型可用类型。

1. 简单的泛型定义使用：

public class GenericFoo<T> {private T foo;public void setFoo(T foo){this.foo = foo;}public T getFoo(){return this.foo;}public static void main(String[] args){//GenericFoo is a raw type, References to generic type GenericFoo<T> should be parameterized.GenericFoo foo = new GenericFoo(); GenericFoo<String> sFoo = new GenericFoo<String>();GenericFoo<Integer> iFoo = new GenericFoo<Integer>();sFoo.setFoo("string foo");
//        sFoo.setFoo(11); //这里只能放置String类型的，放置11在编译时就会报错。iFoo.setFoo(11);}
}

2.定义两个泛型，以及泛型数组的定义使用：

public class GenericFoo2<T,E> {private T foo1;private E foo2;private T[] arrays;public T getFoo1() {return foo1;}public void setFoo1(T foo1) {this.foo1 = foo1;}public E getFoo2() {return foo2;}public void setFoo2(E foo2) {this.foo2 = foo2;}public T[] getArrays() {return arrays;}public void setArrays(T[] arrays) {this.arrays = arrays;}public static void main(String[] args){GenericFoo2<String,Boolean> gf = new GenericFoo2<String,Boolean>();gf.setFoo1("string");gf.setFoo2(false);gf.setArrays(new String[]{"aa","bb"});}
}

3.模仿ArrayList实现集合泛型化：

public class GenericCollection<E> {private Object[] array;private int index;public GenericCollection(){this(10);}public GenericCollection(int capacity){array = new Object[capacity];}public void add(E e){array[index++] = e;}public E get(int index){return (E)array[index];}public static void main(String[] args){GenericCollection<Integer> gc = new GenericCollection<Integer>();for(int i=0;i<10;i++){gc.add(i*2);}for(int i=0;i<10;i++){System.out.println(gc.get(i));}}
}