中軟國(guó)際預(yù)習(xí)材料12 java util包

java.util 掌握HashMap類

java.utilArrayList類掌握HashMap類java.util importDate inthrs,intmin,int publicclass{publicstaticvoidmain(String[]{Datedate=newDate();//獲得當(dāng)前的系統(tǒng)日期和時(shí)間System.out.println("今天的日期是："+date);longtime=date.getTime(); 起以毫秒為單位的時(shí)間(GMT):"+StringstrDate=date.toString();StringstrTime=strDate.substring(11,(strDate.length()-4));strTime=strTime.substring(0,8);}}CalendarCalendar類也是用來(lái)操作日期和時(shí)間的類，但它可以以整Calendar類是抽象類，無(wú)法實(shí)例化，要得到該類對(duì)象只能Calendar對(duì)象提供為特定語(yǔ)言或日歷樣式實(shí)現(xiàn)日期格式化 intget(intvoidset(intfields,intDateObjectvoidCalendarpublicclass{{Calendarcal=Calendar.getInstance();System.out.print(cal.get(Calendar.YEAR"年");System.out.print(cal.get(Calendar.DATE"日");System.out.print(cal.get(Calendar.HOUR)+":");System.out.print(cal.get(Calendar.MINUTE":");cal.add(Calendar.MINUTE,30);Datedate=+}}在顯示日期的時(shí)候，可以使用很多格式，這時(shí)我們就可以RandomRandom類專門用來(lái)生成隨機(jī)數(shù)； intlongRandompublicclass{publicstaticvoidmain(String[]{Randomrand=newfor(inti=0;i<20;i++){intnum=System.out.println(i1+}}} API，API之間可以來(lái)回傳遞集java.util為了滿足不同場(chǎng)合的需要，java.util包中包含有一系列如：ArrayList類、LinkedList類、Vector類、HashMap類集合類中只能存放對(duì)象，而不能存放原始數(shù)據(jù)類型的元素，ArrayList ArrayList ArrayList intvoidObjectset(intindex,ObjectArrayList類示例publicclassArrayListDemo1publicstaticvoidmain(String[]args)ArrayListal=newArrayList();for(inti=0;i<10;i++){Integernum=newInteger(i);

}for(inti0;ial.sizeiIntegertemp=(Integer)(al.get(i));

}al.clear();//清空if(al.isEmpty()){ }else}}}ArrayList類示例publicclassArrayListDemo2publicstaticvoidmain(String[]args)ArrayListalnew al.add("蘋果");al.add("梨子");al.add("香蕉");al.add("西瓜");al.add("榴蓮");for(inti=0;i<al.size();i++){}StringstrnewString(intindex=al.indexOf(str); if(index<0){}elseSystem.out.println(str} for(inti=0;i<al.size();i++){}}}–示例 LinkedList LinkedList LinkedList intvoidObjectset(intindex,Object ObjectLinkedListpublicclassLinkedListDemopublicstaticvoidmain(String[]args)LinkedListllnewLinkedList();//創(chuàng)建空的鏈表for(inti=1;i<=10;i++){Doubletemp=newDouble(Math.sqrt(i));//創(chuàng)建包裝類對(duì)象 }for(inti=0;i<ll.size();i++){}

for(inti=0;i<ll.size();i++){}}}Vector intcapacityIncrement) intvoidObjectset(intindex,Object intvoidseementAt(Objectelem,intvoidVectorpublicclass{publicstaticvoidmain(String[]{Vectorvec=newVector();//創(chuàng)建空的System.out.println(vec.toString());//打印Vectorvec.removeElement("C++");//刪除其中的元素}}HashMap intvoidHashMappublicclassHashMapDemopublicstaticvoidmain(String[]args)HashMaphm=newhm.put("93-07",hm.put("84-12",hm.put("102-20",hm.put("91-04",hm.put("111-17",

//創(chuàng)建空的System.out.println("學(xué)號(hào)91-04的學(xué)生是"+hm.get("91-04"));System.out.println("學(xué)號(hào)84-12的學(xué)生是"+hm.