第六章工具类

1、6-1Programming in Java第六章Java类库6-2Programming in Java是java所有类的父类方法 public Object() java.lang.Objectpublic Class getClass()protected void finalize()无参构造函数，继承必备protected Object clone()对象克隆public boolean equals(Object obj)判断2对象是否相等，相当于=public String toString()对象终结器，对象释放时调用打印输出和转换为字符串时调用-返回类型名地址6-3Progr

2、amming in Java所有类的祖先ObjectObject obj1=new Emloyee(1,张三); class Emloyee int m_EmpNumber; String m_EmpName; Emloyee(int num,String name) m_EmpNumber=num; m_EmpName=name; extends Object父子class ComEmloyee extends Employee int m_Hour; ComEmloyee(int hour,int num,String name) super(num,name);m_Hour=hourOb

3、ject obj1=new ComEmloyee(10,1,张三); 父子6-4Programming in Java例：字符串连接和+的密秘uSystem.out.println(obj1)时会自动调用obj1的toString()函数u“”+obj1 时会自动调用obj1的toString()函数6-5Programming in Java例：字符串连接和+的密秘package javajichu201109.ch6;public class TestObject public static void main(String args) Emloyee e1=new Emloyee(1,张

4、三); System.out.println(e1);class Emloyee int m_EmpNumber; String m_EmpName; Emloyee(int num,String name) m_EmpNumber=num; m_EmpName=name; javajichu201109.ch6.Emloyeec171646-6Programming in Java例：字符串连接和+的密秘如果希望System.out.println(e1);出如下内容：我的名字叫张三，我的编号是1号，该怎么办？class Emloyee int m_EmpNumber; String m_E

5、mpName; Emloyee(int num,String name)m_EmpNumber=num; m_EmpName=name; 答：在Employee中改写(覆盖)toString()方法public String toString() return 我的名字叫+m_EmpName+，我的编号是+m_EmpNumber; 6-7Programming in Java数据类型类shortlongbytefloatdoubleintcharbooleanBooleanCharactorByteShortIntegerLongFloatDouble6-8Programming in Jav

6、a 产生封装类型对象 public Integer(int x) public Integer(String s) 转换成字符串 public String toString() public static String toString(int x) 字符串转换成包装类型 public Integer valueOf(String s)数据类型类6-9Programming in Java字符串转换成基本数据类型 public static int parseInt(String s) public static float parseFloat(String s) public stati

7、c double parseDouble(String s) 数据类型类6-10Programming in Javau负责对应基本数据类型与字符串和其他类型的转换u存储到向量、队列、链表等数据结构中时，需要把基本数据类型包装成对象 数据类型类int x=90; String s=Integer.toBinaryString(x); System.out.println(s);1011010 s=Integer.toHexString(x); System.out.println(s);5a s=Integer.toOctalString(x); System.out.println(s);1

8、32 s=Integer.toString(x); System.out.println(s);906-11Programming in Java6-12Programming in Java没有实例对象 方法(全为静态方法) public static void exit(int status)public static void arrayCopy(Object src, int srcp, Object dst, int dstp,int length) public static long currentTimeMillis() public static void gc()java.

9、lang.System6-13Programming in JavaSystem.out.println(System.currentTimeMillis();6-14Programming in Javapublic final static double E;public final static double PI;public static double abs(double a)public static double acos(double a)public static double exp(double a)public static double floor(double a

10、)public static double random()public static double sqrt(double a)public static double pow(double a,double b).java.lang.Math6-15Programming in Java System.out.println( Math.exp(5); System.out.println( Math.random(); System.out.println( Math.pow(5,6);6-16Programming in Java 构造方法 public String() pubic

11、String(String s) public String(StringBuffer) public String (char value)java.lang.String6-17Programming in JavaString s1; s1=new String(); s1=new String(abcd); char a=new chare,f,g,h; s1=new String(a);abcds1s1efghs16-18Programming in Java获取字符串长度public int length() 判断字符串的前缀和后缀public boolean startsWith

12、(String prefix)public boolean endsWith(String suffix)java.lang.String6-19Programming in Javas1.length( ) s1.startsWith(jk ) s1.endWith(jk )efghs14falsefalse6-20Programming in Java字符串中单个字符查找public int indexOf(int ch)public int indexOf(int ch,int fromIndex)public int lastIndexOf(int ch)public int last

13、IndexOf(int ch,int fromIndex)public char charAt(int index)java.lang.String6-21Programming in Javas1.charAt(2) s1. indexOf(e)s1. indexOf(e,1)efghs1g0-16-22Programming in Java字符串中子串的查找public int indexOf(String str)public int indexOf(String str,int fromIndex)public int lastIndexOf(String str)public int

14、 lastIndedOf(String str, int fromIndex)public String substring(int be,int end)java.lang.String6-23Programming in Javas1.indexOf(ef)s1.indexOf(ef“,1)s1.lastIndexOf(ef“,1)s1.substring(0,2)efghs10-1efefs12efg6-24Programming in Java将字符串编程字符数组 public void getChars(int be,int en, char dst,int dstB)替换字符串中的

15、字符 public String replace(char so,char dst)字符串大小写转换 public String toLowerCase() public String toUpperCase()java.lang.String6-25Programming in Javachar a=new char10; s1.getChars(0,3,a,0); String s2=s1. replace(e,a)s2=s1. toUpperCase()efghs1feagefghs1afghs2efghs1EFGHs26-26Programming in Java比较两个字符串publ

16、ic int compareTo(String anotherString)public boolean equals(Object anObject)public boolean equalsIgnore(String anotherString) 连接字符字串public String concat(String str)基本数据类型转换为字符串 public static String valueOf(X x)java.lang.String6-27Programming in JpareTo(dddddddddddd)s1. equals(“efgh”)s1. equalsIgnore

17、 (“EFGH”)String s3=s1. concat(“ijk”);String s4= String.valueOf(56);1efghs1truetrueefghs1efghijks356s46-28Programming in Java实例 编程判断一个字符串是否是回文6-29Programming in Java 构造方法public StringBuffer()public StringBuffer(int length)public StringBuffer(String str) 字符串变量的扩充、修改与操作public StringBuffer append(X,x)pu

18、blic StingBuffer insert(int index,X x) public StringBuffer deleteCharAt(int s) public StringBuffer reverse()public StringBuffer setCharAt(int in,char ch)java.lang.StringBuffer6-30Programming in JavaStringBuffer s1=new StringBuffer ();StringBuffer s2=new StringBuffer (abcd);StringBuffer s3=new String

19、Buffer (6);s2.insert (1,gggg);s2.setCharAt (1,d); s3.append(odj) ; s1abcds2 s3aggggbcds2adgggbcds2odjs36-31Programming in Java s2.deleteCharAt(1);s2.reverse()agggbcds2dcbgggas26-32Programming in Javapublic class UseComLparameterpublic static void main(String args)int a1,a2,a3;if(args.length2)System.

20、out.println(运行本程序应该提供两个命令行参数);System.exit(0);a1=Integer.parseInt(args0);a2=Integer.parseInt(args1);a3=a1*a2;System.out.println(a1+与+a2+相乘的积为:+a3);命令行参数6-33Programming in Java数组1.一维数组1）定义（分三步走） 声明数组 int a; int b; 创建数组空间 a=new int5; 赋初值6-34Programming in Java2)性质Length下标是Object类的对象3）数组操作元素的下标访问数组元素拷贝S

21、ystem.arraycopy (Object s,int bes, Object d, int bed,int length);数组赋值6-35Programming in Java /数组定义int e;/声明数组e=new int 5;/内必须有元素个数for(int i=0;ie.length ;i+)/元素初始化ei=i;6-36Programming in Javafor(int i=0;ie.length ;i+)/属性lengthSystem.out .print (ei+ );int a=1,2,3,4;/直接初始化for(int j=0;ja.length ;j+)Syst

22、em.out .print (n+aj+ );int d=new int 5,6,7,8;/内无元素个数6-37Programming in JavaEmployee c=new Employee (),new Employee ();/对象数组/ c=new Employee 3;for(int i=0;ic.length ;i+)/ci=new Employee ();System.out .println (ci.getClass ().getName (); 6-38Programming in Java/数组符值是把同一数组空间取了一个别名a=d;for(int i=0;ia.len

23、gth ;i+)System.out .println (a+i+=+ai+nd+i+=+di);a0=56;System.out .println (a0=+a0+nd0=+d0);6-39Programming in Java/数组拷贝System.arraycopy (d,2,a,0,2);for(int i=0;ia.length ;i+)System.out .println (a.length ); /a+i+=+ai+nd+i+=+di);6-40Programming in Java2.二维数组1)定义2)性质实质是一维数组的一维数组length是行数3)操作二维数组元素下标访

24、问元素交换6-41Programming in Java/二维数组int f=2,3,4,4,5,6;System.out .println (f.length=+f.length );/二维数组是数组的数组int g=new int 45;/创建多维数组空间时可把行和列分开g=new int 6;for(int i=0;ig.length ;i+)gi=new int i+1;234456 6-42Programming in JavaEmployee x=new Employee (),new Employee (),new Employee (),new Employee (); 6-4

25、3Programming in Javafor(int j=0;jx.length ;j+)for(int i=0;ixj.length ;i+)/ci=new Employee ();System.out .println (xij.getClass ().getName ();6-44Programming in Java/数组元素交换int t=f0;f0=f1;f1=t;for(int i=0;if.length ;i+)for(int j=0;jfi.length ;j+)System.out .print (fij);System.out .println ();6-45Progr

26、amming in Java 功能：实现变长对象数组 构造函数 public Vector( int initialCapacity, int capacityIncrement ) public Vector( int initialCapacity ) public Vector() 向向量序列中添加元素 public void addElement(Object obj ) public void insertElementAt( Object obj, int index ) java.util.Vector6-46Programming in JavaVector v1=new Ve

27、ctor ();Vector v2=new Vector (4);Vector v3=new Vector (2,5);/2为原始序列中包含元素个数,5为一次性追加元素个数v3.addElement (aaaa);v3.addElement (Integer.valueOf (56);v1v2aaaav3aaaa56v36-47Programming in Javav3.insertElementAt (bbbb,0);/insertElementAt只能向已存在的序列中插入元素v3.setElementAt (cccc ,1);/setElementAt只能修改序列中已存在的元素bbbb56v3aaaacccc56v3aaaa6-48Programmi