Collections工具类和泛型
Collections和Collection
Collections和Collection是不同的,Collections是工具类,用来操作集合的,而Collection是集合接口。Collections中有一系列的静态方法用来操作集合,但是不能更改集合内容。比如不能set()不能remove()元素,可以替换全部元素或者添加同一个元素。
static List<String> list =Arrays .asList("one Two three Four five six one".split( " "));//Two 和Four有意为之~
public static void main (String[] args) {
// TODO Auto-generated method stub
System.out .println (list) ;
System.out .println ("max="+ Collections. max( list));
System.out .println ("min="+ Collections. min( list));
System.out .println ("忽略大小写max="+ Collections. max(
list, String. CASE_INSENSITIVE_ORDER));
System.out .println ("忽略大小写min="+ Collections. min(
list, String. CASE_INSENSITIVE_ORDER));
List<String > sublist =Arrays .asList("Four five six" .split (" ")) ;
System.out .println ("indexOfSublist=="+
Collections .indexOfSubList(list , sublist ));
System.out .println ("lastIndexOfSubList=="+
Collections .lastIndexOfSubList (list, sublist)) ;
Collections .replaceAll(list , "one", "YO") ;
System .out.println( "replace"+list );
Collections .reverse(list );
System.out .println ("resever"+ list);
Collections .shuffle(list ,new Random(47 ));
System.out .println ("shuffle"+ ""+list) ;
List<String > source =Arrays .asList("dong ting lake" .split (" ")) ;
Collections .copy(list , source );
System.out .println ("copy"+ ""+list) ;
Collections .fill(list , "pop");
System.out .println ("fill"+ ""+list) ;
System.out .println ("frequency"+
Collections .frequency(list , "pop"));
}
}
/*[one,
Two, three, Four, five, six, one]
max=three
min=Four
忽略大小写max=Two
忽略大小写 min=five
indexOfSublist==3
lastIndexOfSubList==3
replace[YO,
Two, three, Four, five, six, YO]
resever[YO,
six, five, Four, three, Two, YO]
shuffle[three,
five, six, YO, Four, Two, YO]
copy[dong, ting,
lake, YO, Four, Two, YO]
fill[pop,
pop, pop, pop, pop, pop, pop]
frequency7*/
泛型
泛型应用在泛型接口,泛型类和泛型方法中,主要作用是使参数类型化,将运行时参数不匹配错误转移到编译时期,避免强制类型转换。
泛型接口比较好理解,就是说这个接口的实现类有许多的类型,再写这个类的时候,并不知道会有什么类型的类来实现这个接口。
interface Solution< T> {
public void say ();
}
实现这个接口的类可以是泛型的,也可以是具体类型的,比如下面这个类是具体类型的,String。
class GenericTest implements Solution< String> {
public static void main ( String[] args ) {
Solution <String > gt = new GenericTest ();
实现这个接口的类依然是泛型的类。
class GenericTest< T> implements Solution <T >{
public static void main ( String[] args ) {
Solution <String > gt = new GenericTest <String >() ;
Solution <Integer > ss= new GenericTest <Integer >() ;
泛型类和泛型方法
//泛型类
class Solution3< V, T> {
//利用泛型的构造函数
public Solution3( V
name, T other ) {
super ();
this. name = name;
this. other = other;
}
public V
getName() {
return name ;
}
public void setName (V
name ) {
this. name = name;
}
public T
getOther() {
return other ;
}
public void setOther (T
other ) {
this. other = other;
}
V name;
T other;
}
public class GenericC {
public static void main ( String[] args ) {
//由于这个类的构造方法用到了泛型,那么我们可以在泛型范围内
//使用不同的类型来构造对象,没有使用泛型之前你可能无法这么做
//String,String类型的构造函数
Solution3 <String ,String > ss = new Solution3 <String , String >( "方案" , "目标" );
//String,integer类型的构造函数
Solution3 <String ,Integer > si = new Solution3 <String , Integer >( "方案" , 3 );
System .out .println ( "String+Sting"+ ss. getName ()+ ss. other) ;
System .out .println ( "String+Integer"+ si. getName ()+ si. other) ;
/*String+Sting方案目标
String+Integer方案3*/
使用通配符
通配符"?"
class Jiangyou{
}
class Solution5< T> {
T t;
public Solution5( T
t ) {
super ();
this. t = t;
}
}
public class GenericD {
//一个使用了泛型类的对象的方法,将泛型对象定义为通配符“?”
public static void function ( Solution5<?> so ){
System . out. println( "方案:
" +so .t );
}
public static void main ( String[] args ) {
//通配符"?"的权限很大
Solution5 <String > so5 = new Solution5 <String >( "目标" );
//可以是Number基本数据类型
Solution5 <Number > so7 = new Solution5 <Number >( 6 );
//甚至是Object,这里用了个酱油类
Solution5 <Jiangyou > so6 = new Solution5 <Jiangyou >( new Jiangyou()) ;
function( so5 );
function( so6 );
function( so7 );
/* 方案:
目标
方案: [email protected]
方案:
6*/
上限限定
//一个使用了泛型类的对象的方法,将泛型类型上限定为Number的类型
public static void function ( Solution5<? extends Number> so ){
System . out. println( "方案:
" +so .t );
}
public static void main ( String[] args ) {
//Number及其子类都可以调用function方法
Solution5 <Integer > solution = new Solution5 <Integer >( 3 );
Solution5 <Double > solution1 = new Solution5 <Double >( 3. 0 );
//String类型的Solution无法调用function方法
Solution5 <String > solution2= new Solution5< String> ("mubiao" );
function( solution );
function( solution1 );
/* 方案:
3
方案:
3.0*/
下限限定
//一个使用了泛型类的对象的方法,将泛型类型下限定为Integer的类型
public static void function ( Solution5<? super Integer> so ){
System . out. println( "方案:
" +so .t );
}
public static void main ( String[] args ) {
//Integer及其父类都可以调用function方法
Solution5 <Integer > solution = new Solution5 <Integer >( 3 );
//Double不是Integer的父类无法调用function方法
Solution5 <Double > solution1= new Solution5< Double> (3 .0 );
//Object类型的Solution调用function方法
Solution5 <Object > solution2 = new Solution5 <Object >( "mubiao" );
function( solution );
//function(solution1);
function( solution2 );
/* 方案:
3
方案: mubiao*/
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