Arrays,Integer,Character,Math,Random,System,BigDecimal, Date ,
Arrays:针对数组操作的工具类
1.toString 把任何类型的数组转为字符串
2.sort:排序
3.public static int binarySearch(int[] arr,int key) :二分查找
Integer
1.构造方法:
1 public Integer(int value)
2 public Integer(String s)
2.成员方法
int->String
方式1:int num=100; String s=""+num;
方式2:String s=String.valueOf(num);
方式3:int->Integer->String
Integer i=new Integer(num); String s=i.toString();
方式4:public static String toString(int i)
String s=Integer.toString(num);
String->int
方式1:String->Integer->int
Integer i=new Integer(s); int x=i.intValue();
方式2:public static int parseInt(s)
int x=Integer.parseInt(s);
Character
1.构造方法 public Character(char value)
2.成员方法
isUpperCase(char ch)
isLowerCase(char ch)
isDigit(char ch):判断是不是数字字符
toUpperCase(char ch)
toLowerCase(char ch)
Math
1. E PI
2. 成员方法 abs:绝对值 ceil:向上取整 floor:向下取整 max min pow(a,b) 次幂 random round:四舍五入 sqrt:正平方根
Random
public int nextInt() public int nextInt(int n)
System
currentTimeMillis() arraycopy
BigDecimal
构造方法:public BigDecimal(String val)
add subtract multiply divide divide(BigDecimal divisor ,int scale , int roundingMode):商,几位小数,如何取舍
Date
构造方法:
public Date()
public Date(long date)
成员方法
public long getTime()
public void setTIme()
SimpleDateFormat
format parse
Calender
public int get(int field)
1 Calendar now=Calendar.getInstance(); 2 3 int year=now.get(Calendar.YEAR); 4 5 int month=now.get(Calendar.MONTH)+1; 6 7 int date=now.get(Calendar.DATE); 8 9 System.out.println(year+"--"+month+"---"+date);
1 Calendar now=Calendar.getInstance(); 2 3 now.add(Calendar.YEAR, -3); 4 5 int year=now.get(Calendar.YEAR); 6 int month=now.get(Calendar.MONTH); 7 int date=now.get(Calendar.DATE); 8 9 10 11 System.out.println(year);
1 package hello; 2 3 import java.io.BufferedOutputStream; 4 import java.io.File; 5 import java.io.FileInputStream; 6 import java.io.FileNotFoundException; 7 import java.io.FileOutputStream; 8 import java.io.IOException; 9 import java.io.InputStreamReader; 10 import java.io.OutputStreamWriter; 11 import java.text.SimpleDateFormat; 12 import java.util.Calendar; 13 import java.util.Date; 14 import java.util.HashSet; 15 import java.util.Random; 16 import java.util.TreeSet; 17 18 public class Test02{ 19 public static void main(String[] args) throws Exception { 20 Calendar now=Calendar.getInstance(); 21 int year=2015; 22 now.set(year, 2,1); 23 now.add(Calendar.DATE, -1); 24 System.out.println(now.get(Calendar.DATE)); 25 26 } 27 }