一、根本数据类型的包装类
包装类是将根本数据类型封装成一个类，蕴含属性和办法
应用：
在应用过程中，会波及到主动装箱和主动拆箱
装箱：将根本数据类型转换成包装类型
拆箱：将包住类型转换成根本数据类型
示例
package com.msbline.basic.common;public class IntegerDemo { public static void main(String[] args) { int a = 10; Integer i = new Integer(10); //通过办法进行类型的转换 Integer i2 = Integer.valueOf(a); int i3 = i2.intValue(); System.out.println(a == i); Integer b1 = 100; Integer b2 = 100; Integer b3 = 200; Integer b4 = 200; //这两个后果的不统一，是因为在主动拆箱的时候, //如果value不在规定范畴内（-128到127）的时候，会 new Interger, //导致比拟的时候两个地址不统一 //Interger 中主动拆箱的办法： //public static Integer valueOf(int i) { // if (i >= IntegerCache.low && i <= IntegerCache.high) // return IntegerCache.cache[i + (-IntegerCache.low)]; // return new Integer(i); // } System.out.println(b1 == b2);//true System.out.println(b3 == b4);//false }}二、字符串相干类
1、不可变字符序列：String
留神：
1、常量池在jdk1.7之后放在了对空间中
2、字符串的实质
--字符串的实质是字符数组或者叫字符序列
--String类应用final润饰，不能够被继承
--应用equals办法比拟的是字符数组的每个地位的值
示例
package com.msbline.basic.common;public class StringDemo { public static void main(String[] args) { String str = "abc"; String str1 = new String("abc"); System.out.println(str == str1); System.out.println(str.equals(str1)); str1 = str1.intern(); System.out.println(str == str1); System.out.println(str1.charAt(0)); System.out.println(str1.concat("def")); System.out.println("-------------"); String a = "abc"; String b = "def"; String c = "abcdef"; String d = a+b;// String d = (a+b).intern(); String e = "abc"+"def"; System.out.println(c == d);//false System.out.println(c == e);//true System.out.println("-------------"); String f = "a"+"b"+"c";//一个对象 //如下则是4个对象 String a1 = "a"; String a2 = "b"; String a3 = "c"; String f1 = a1+a2+a3; }}2、可变字符序列：StringBuffer、StringBuilder
StringBuffer 线程平安 效率低
StringBuilder 线程不平安 效率高
示例
package com.msbline.basic.common;public class StringBufferDemo { public static void main(String[] args) { StringBuffer stringBuffer = new StringBuffer(); stringBuffer.append(1) .append(1.234) .append("abcaaaaaaaaaaaaa") .append(true); System.out.println(stringBuffer); System.out.println(stringBuffer.charAt(1)); System.out.println(stringBuffer.length()); System.out.println(stringBuffer.capacity()); System.out.println("-----------------------------"); //StringBuilder与StringBuffer应用大抵一样 StringBuilder stringBuilder = new StringBuilder(); }}小结
三、工夫解决相干类
1、Date、DateFormat、SimpleDateFormat、Calender
示例
package com.msbline.basic.common;import java.text.DateFormat;import java.text.ParseException;import java.text.SimpleDateFormat;import java.util.Calendar;import java.util.Date;public class DateDemo { public static void main(String[] args) throws ParseException { Date date = new Date(); System.out.println(date); //过期的办法 System.out.println(date.getYear()); //返回以后日期的毫秒值 System.out.println(date.getTime()); //yyyy-MM-dd HH:mm:ss DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); //将date类依照标准转换为字符串格局 String str = dateFormat.format(date); System.out.println(str); //将字符串转换成对应的日期类 Date date1 = dateFormat.parse("2010-10-10 20:20:20"); System.out.println(date1); System.out.println("-----------------------------------------"); Calendar calendar = Calendar.getInstance(); System.out.println(calendar); //设置指定工夫的日历类 calendar.setTime(date1); System.out.println(calendar); System.out.println(calendar.get(Calendar.YEAR)); System.out.println(calendar.get(Calendar.MONTH)); System.out.println(calendar.get(Calendar.DAY_OF_MONTH)); System.out.println(calendar.get(Calendar.HOUR_OF_DAY)); System.out.println(calendar.get(Calendar.MINUTE)); System.out.println(calendar.get(Calendar.SECOND)); }}四、Math类
示例
package com.msbline.basic.common;public class MathDemo { public static void main(String[] args) { System.out.println(Math.abs(-1)); System.out.println(Math.sqrt(2)); //向上取整 System.out.println(Math.ceil(3.14)); //向下取整 System.out.println(Math.floor(3.14)); //2的3次方 System.out.println(Math.pow(2,3)); }}五、枚举类 jdk1.5
示例
package com.msbline.basic.common;public enum Event { LAUNCH("launch"),PAGEVIEW("pageview"),EVENT("event"); private String name; Event(String name){ this.name = name; } public void show(){ System.out.println(this.name); Event[] ee = values(); for(int i = 0; i < ee.length; i++){ System.out.println(ee[i].name); } }}package com.msbline.basic.common;public enum Gender { 男,女}package com.msbline.basic.common;public class Test { public static void main(String[] args) { Gender gender = Gender.女; Gender gender1 = Gender.男; Event event = Event.LAUNCH; System.out.println(event.name()); event.show(); }}