API补习之java.util包

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

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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();

}

}

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());