class="article_content clearfix">
class="htmledit_views">
1.Date
class="language-java">import java.util.Date;
public class DateTimeDisplay {
Date objDate;
DateTimeDisplay() {
objDate = new Date();
}
void display() {
String strDate, strTime = "";
System.out.println("今天的日期是:" + objDate);
long time = objDate.getTime();
System.out.println("自1970年1月1日起以毫秒为单位的时间(GMT):" + time);
strDate = objDate.toString();
strTime = strDate.subclass="tags" href="/tags/STRING.html" title=string>string(11, (strDate.length() - 4));
strTime = "时间:" + strTime.subclass="tags" href="/tags/STRING.html" title=string>string(0, 8);
System.out.println(strTime);
}
}
public class DateTest2 {
public DateTest2() {
}
public static void main(String[] args) {
DateTimeDisplay objDateTime=new DateTimeDisplay();
objDateTime.display();
}
}
输出: 今天的日期是:Fri Jul 04 15:02:51 CST 2008 自1970年1月1日起以毫秒为单位的时间(GMT):1215154971375 时间:15:02:51
例子2 格式化时间
class="language-java">package my;
import java.util.Date;
import java.util.Locale;
import java.text.DateFormat;
class DateTime {
Date objDate;
DateTime() {
objDate = new Date();
}
void convert() {
DateFormat simpleFormat =DateFormat.getDateInstance(DateFormat.LONG, Locale.CHINESE);
String strDate = objDate.toString();
System.out.println("当前日期： " + strDate);
System.out.println("/n格式化后： "
+ simpleFormat.format(objDate));
}
}
class DateTimeTest {
protected DateTimeTest() {
}
public static void main(String[] args) {
DateTime objDateTime = new DateTime();
objDateTime.convert();
}
}
2 Calendar类是抽象类,无法像Date一样实例化 objCalendar=Calendar.getInstance();
3 Random类 new Random().nextFloat(); 再生成一个0.0到1.0之间的随机数 或者用Math.random()来产生0.0到1.0之间的随机数 4.ArrayList类
class="language-java">
import java.util.ArrayList;
import java.util.Random;
import java.util.List;
import java.util.Collections;
class PlayersList {
ArrayList playerArray;
List subListObj;
List otherListObj;
PlayersList() {
playerArray = new ArrayList();
subListObj = new ArrayList();
}
void add() {
for (int ctr = 0; ctr < 5; ctr++) {
playerArray.add(new Integer(ctr));
}
playerArray.add("Martina");
playerArray.add("Serena");
playerArray.add("Venus");
playerArray.add("Serena");
System.out.println(playerArray);
}
void display() {
for (int ctr = 0; ctr < playerArray.size(); ctr++) {
System.out.print(" " + playerArray.get(ctr));
}
System.out.println();
}
void search() {
System.out.println("字符串 Serena 第一次出现在位置 "+playerArray.indexOf("Serena"));
System.out.println("字符串 Serena 第一次出现在位置 "+playerArray.lastIndexOf("Serena"));
}
/**
* 从 ArrayList 提取一个子列表
*/
void extract() {
subListObj = playerArray.subList(5, playerArray.size());
System.out.println("索引 5 至" + playerArray.size() + "的新子列表为: " + subListObj);
}
/**
* 随机更改顺序
*/
void shuffle() {
System.out.println("播放器列表 (之前): " + playerArray);
Collections.shuffle(playerArray, new Random());
System.out.println("播放器列表 (之后): " + playerArray);
}
/**
* 对 ArrayList 进行排序.
*/
void sort() {
System.out.println("排序前： " + playerArray);
Collections.sort(bookArray);
System.out.println("排序后： " + playerArray);
}
/**
* 反转 ArrayList.
*/
void reverse() {
System.out.println("反转前： " + playerArray));
Collections.reverse(bookArray);
System.out.println("反转后： " + playerArray));
}
void copy() {
System.out.println("playerArray 是否为空？ " + playerArray.isEmpty());
System.out.println("playerArray （之前）： " + playerArray);
bookCopyObj = new ArrayList(bookArray);
System.out.println("otherListObj （之后）： " + otherListObj);
}
}
class PlayerListTest {
public static void main(String[] args) {
PlayersList playerObj = new PlayersList();
playerObj.add();
playerObj.display();
playerObj.search();
playerObj.extract();
playerObj.shuffle();
playerObj.sort();
playerObj.reverse();
playerObj.copy();
}
}
4.2LinkedList类 方法addLast(); removeFirst(); getFirst();获得队列第一个元素.
输出: [dog, dog, cat, aat, Aat, b4] [dog, cat, b4, Aat, aat] 是随机的顺序
4.3 HashMap类 键值对照表
class="language-java">import java.util.*;
public class PrintingContainers {
static Map fill(Map m) {
m.put("dog2", "Bosco"); //dog2是key,Bosco是value 用Map.Entry来取键值
m.put("dog", "Spot");
m.put("cat", "Rags");
return m;
}
public static void main(String[] args) {
System.out.println(fill(new HashMap()));
}
}
输出: {dog2=Bosco, dog=Spot, cat=Rags}
5. Vector类
class="language-java">import java.util.Vector;
class PreciousStones {
Vector preciousVector;
PreciousStones() {
preciousVector = new Vector();
}
void add() {
preciousVector.addElement("翡翠");
preciousVector.addElement("黄晶");
preciousVector.addElement("绿宝石");
preciousVector.addElement("祖母绿");
}
void insert() {
preciousVector.insertElementAt("钻石" , 0);
preciousVector.insertElementAt("猫眼石" , 4);
}
void display(String title) {
int count = 0;
while (count < preciousVector.size()) {
System.out.print(preciousVector.elementAt(count));
count++;
if (count < preciousVector.size()) {
System.out.print(", ");
}
}
}
void search() {
if (preciousVector.contains("钻石")) {
System.out.println("在索引 " + preciousVector.indexOf("钻石") + " 中找到钻石");
}
}
void remove() {
preciousVector.removeElement("黄晶");
System.out.println("删除黄晶后的内容: ");
int count = 0;
while (count < preciousVector.size()) {
System.out.print(preciousVector.elementAt(count));
count++;
if (count < preciousVector.size()) {
System.out.print(", ");
}
}
}
void otherDetails() {
System.out.println("/n第一个元素 = " + preciousVector.firstElement());
System.out.println("默认容量 = " + preciousVector.capacity());
}
}
class PreciousStoneTest {
public static void main(String [] args) {
PreciousStones objPrecious = new PreciousStones();
objPrecious.add();
objPrecious.display("显示内容");
objPrecious.insert();
objPrecious.display("显示插入后的内容");
objPrecious.search();
objPrecious.remove();
objPrecious.otherDetails();
}
}
6. Iterator类 hasNext() next() remove()
class="language-java">list和set的区别比较的例子
import java.util.*;
public class PrintingContainers {
static Collection fill(Collection c) {
c.add("dog");
c.add("dog");
c.add("cat");
c.add("aat");
c.add("Aat");
c.add("b4");
return c;
}
public static void main(String[] args) {
//List以特定顺序存储一组元素
//set元素是不能重复的
System.out.println(fill(new ArrayList()));
System.out.println(fill(new HashSet()));
}
}
