1、第八章 Java 實(shí) 用 包,教學(xué)目標(biāo),程序設(shè)計(jì)中常用的Java 類: Math String StringBuffer StringTokenizer Vector Enumeration,常用的類和包對(duì)應(yīng)關(guān)系 :,包名 類 包名 類 Java.langString javax.swing Jbutton Wrapper classes Jlabel Math Jtextfield . Java.util Calendar java.io InputStream Date OutputStream Vector Java.text DateFormat Java.awt Graphics B

2、utton Label TextField,7.1 Math類,java.lang.Math是標(biāo)準(zhǔn)的數(shù)學(xué)函數(shù)類:封裝了一些數(shù)學(xué)函數(shù)和常量 如：三角函數(shù)、指數(shù)函數(shù)、隨機(jī)數(shù)函數(shù)等。 java.lang.Math類是final型的，不能被子類化或?qū)嵗?Math類的所有方法和常量是靜態(tài)的。,public class MathDemo public static void main(String args) System.out.println(Math.E=+Math.E); /輸出常量e System.out.println(Math.round(Math.E)=+Math.round(Math

3、.E); /四舍五入取整 System.out.println(Math.PI=+Math.PI); /輸出常量p /輸出大于等于e的最小雙精度數(shù) System.out.println(ceil(E)=+Math.ceil(Math.E); /輸出小于等于e的最大雙精度數(shù) System.out.println(floor(E)=+Math.floor(Math.E); /將雙精度值p 轉(zhuǎn)化為一個(gè)整數(shù)值,輸出double型 System.out.println(rint(PI)=+Math.rint(Math.PI); System.out.println(lnE=+Math.log(Math.

4、E); / 計(jì)算e的自然對(duì)數(shù)值 System.out.println(sin(pi/4)=+Math.sin(Math.PI/4); /計(jì)算p /4的正弦值 System.out.println(Math.random(); /產(chǎn)生0到1之間的double型數(shù) System.out.println(int)(100*Math.random()+1); /產(chǎn)生1到100之間的整數(shù) ,輸出結(jié)果：,7.2 字符串類String,String 由字符組成的序列 可包含字母, 數(shù)字等. 是類 String的對(duì)象 一個(gè)String 的對(duì)象一旦創(chuàng)建后, 其內(nèi)容不能被改變,又稱常量字符串,字符串類String

5、,7.2.1 String的構(gòu)造函數(shù) 7.2.2 String的方法,7.2.1 String構(gòu)造函數(shù),表7-1String類的常見構(gòu)造函數(shù),例7-1的程序演示了String類的常見的6個(gè)構(gòu)造函數(shù)的使用。 /StringConstructors.java import javax.swing.*; public class StringConstructors public static void main( String args ) char charArray = b, i, r, t, h, , d, a, y ; byte byteArray = ( byte ) n, ( byte

6、 ) e, ( byte ) w, ( byte ) , ( byte ) y, ( byte ) e, ( byte ) a, ( byte ) r ; String s = new String( hello );,7.2.1 String構(gòu)造函數(shù)（續(xù)）,7.2.1 String構(gòu)造函數(shù)（續(xù)）,String s1 = new String(); String s2 = new String( s ); String s3 = new String( charArray ); String s4 = new String( charArray, 6, 3 ); String s5 = new

7、 String( byteArray, 4, 4 ); String s6 = new String( byteArray ); String output = s1 = + s1 + ns2 = + s2 + ns3 = + s3 + ns4 = + s4 + ns5 = + s5 + ns6 = + s6; JOptionPane.showMessageDialog( null, output, String類構(gòu)造函數(shù)的使用, JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); ,分別調(diào)用String類的六個(gè)構(gòu)造函數(shù),7.2.2 Str

8、ing的方法,表7-2 String類的常用方法,7.2.2 String方法（續(xù)）,7.2.2 String方法（續(xù)）,例7-2 String類的length、charAt和getChars方法的使用 /StringMiscellaneous.java import javax.swing.*; public class StringMiscellaneous public static void main( String args ) String s1 = hello there; char charArray = new char 5 ; String output = s1: + s

9、1; output += nLength of s1: + s1.length(); output += nThe string reversed is: ; for ( int count = s1.length() - 1; count = 0; count- ) output += s1.charAt( count ) + ; s1.getChars( 0, 5, charArray, 0 );,7.2.2 String的方法（續(xù)）,調(diào)用String類的length方法,調(diào)用String類的charAt方法,調(diào)用String類的getChars方法,7.2.2 String方法（續(xù)）,o

10、utput += nThe character array is: ; for ( int count = 0; count charArray.length; count+ ) output += charArray count ; JOptionPane.showMessageDialog( null, output, String類的length、charAt和getChars方法的使用, JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); ,下面的例子通過使用String類的equals、equalsIgnoreCase、compa

11、reTo方法來進(jìn)行字符串的比較。 例7-3字符串的比較,7.2.2 String方法（續(xù)）,7.2.2 String方法（續(xù)）,/StringCompare.java import javax.swing.JOptionPane; public class StringCompare public static void main( String args ) String s1 = new String( hello ); String s2 = goodbye; String s3 = Happy Birthday; String s4 = happy birthday; String o

12、utput = s1 = + s1 + ns2 = + s2 + ns3 = + s3 + ns4 = + s4 + n;,7.2.2 String方法（續(xù)）,if ( s1.equals( hello ) ) output += s1 equals hellon; else output += s1 does not equal hellon; if ( s3.equalsIgnoreCase( s4 ) ) output += s3 equals s4n; else output += s3 does not equal s4n;,調(diào)用String類的equals方法判斷字符串是否相等,調(diào)

13、用String類的equalsIgnoreCase方法在不區(qū)分大小寫的情況下判斷兩字符串是否相等,7.2.2 String方法（續(xù)）,output += pareTo( s2 ) is + pareTo( s2 ) + pareTo( s1 ) is + pareTo( s1 ) + pareTo( s1 ) is + pareTo( s1 ) + pareTo( s4 ) is + pareTo( s4 ) + pareTo( s3 ) is + pareTo( s3 ) + n; JOptionPane.showMessageDialog( null, output, 字符串的比較, JO

14、ptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); ,調(diào)用String類的compareTo方法進(jìn)行兩字符串的大小比較,下面的例子通過調(diào)用String類的indexOf和lastIndexOf方法來完成定位字符串中的字符和子字符串。 例7-4 字符串檢索,7.2.2 String方法（續(xù)）,7.2.2 String方法（續(xù)）,/StringIndexMethods.java import javax.swing.*; public class StringIndexMethods public static void main( String

15、args ) String letters = abcdefghabcdefgh; String output = c is located at index + letters.indexOf( c ); output += na is located at index + letters.indexOf( a, 1 ); output += n$ is located at index + letters.indexOf( $ );,調(diào)用String類的indexOf方法定位某個(gè)字符在字符串中第一次出現(xiàn)的位置,7.2.2 String方法（續(xù)）,output += nLast c is l

16、ocated at index + letters.lastIndexOf( c ); output += nLast a is located at index + letters.lastIndexOf( a, 10 ); output += nLast $ is located at index + letters.lastIndexOf( $ ); output += ndef is located at index + letters.indexOf( def ); output += ndef is located at index + letters.indexOf( def,

17、7 ); output += nhello is located at index + letters.indexOf( hello );,調(diào)用lastIndexOf方法定位某個(gè)字符在字符串中最后一次出現(xiàn)的位置,調(diào)用indexOf方法定位某個(gè)子字符串在字符串中第一次出現(xiàn)的位置,7.2.2 String方法（續(xù)）,output += nLast def is located at index + letters.lastIndexOf( def ); output += nLast def is located at index + letters.lastIndexOf( def, 25 );

18、 output += nLast hello is located at index + letters.lastIndexOf( hello ); JOptionPane.showMessageDialog( null, output, 字符串檢索, JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); ,調(diào)用lastIndexOf方法定位某個(gè)子字符在字符串中最后一次出現(xiàn)的位置,例7-5 字符串截取 通過調(diào)用String類的substring方法來實(shí)現(xiàn)在字符串中提取一個(gè)子字符串,7.2.2 String方法（續(xù)）,7.2.2 String方

19、法（續(xù)）,/SubString.java import javax.swing.*; public class SubString public static void main( String args ) String letters = abcdefghabcdefgh; String output = Substring from index 10 to end is + + letters.substring( 10 ) + n; output += Substring from index 3 up to 6 is + + letters.substring( 3, 6 ) + ;

20、 JOptionPane.showMessageDialog( null, output, 字符串截取, JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); ,調(diào)用substring方法在字符串中提取一個(gè)子字符串,String valueOf methods,staticString valueOf(booleanb) Returns the string representation of the boolean argument. 例子: boolean booleanValue = true; String.valueOf( bool

21、eanValue ); /“true”,import javax.swing.*; public class StringValueOf public static void main( String args ) char charArray = a, b, c, d, e, f ; boolean booleanValue = true; char characterValue = Z; int integerValue = 7; long longValue = 10000000L; float floatValue = 2.5f; / f suffix indicates that 2

22、.5 is a float double doubleValue = 33.333; Object objectRef = hello; / assign string to an Object reference String output = char array = + String.valueOf( charArray ) + npart of char array = + String.valueOf( charArray, 3, 3 ) + nboolean = + String.valueOf( booleanValue ) + nchar = + String.valueOf(

23、 characterValue ) + nint = + String.valueOf( integerValue ) + nlong = + String.valueOf( longValue ) + nfloat = + String.valueOf( floatValue ) + ndouble = + String.valueOf( doubleValue ) + nObject = + String.valueOf( objectRef );,JOptionPane.showMessageDialog( null, output, String valueOf methods, JO

24、ptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); / end class StringValueOf,7.3 StringBuffer類,Class StringBuffer When String object is created, its contents cannot change i.e., constant strings Used for creating and manipulating dynamic string data i.e., modifiable strings Can store characters base

25、d on capacity Capacity expands dynamically to handle additional characters Uses operators + and += for String concatenation,7.3 StringBuffer類,7.3.1 StringBuffer構(gòu)造函數(shù) 7.3.2 StringBuffer類的方法,7.3.1 StringBuffer構(gòu)造函數(shù),表7-3StringBuffer類的構(gòu)造函數(shù),例7-6 StringBuffer類的構(gòu)造函數(shù)的使用,7.3.1 StringBuffer構(gòu)造函數(shù)（續(xù)）,7.3.1 StringB

26、uffer構(gòu)造函數(shù)（續(xù)）,/StringBufferConstructors.java import javax.swing.*; public class StringBufferConstructors public static void main( String args ) StringBuffer buffer1 = new StringBuffer(); StringBuffer buffer2 = new StringBuffer( 10 ); StringBuffer buffer3 = new StringBuffer( hello ); String output = b

27、uffer1 = + buffer1.toString() + + nbuffer2 = + buffer2.toString() + + nbuffer3 = + buffer3.toString() + ; JOptionPane.showMessageDialog( null, output, StringBuffer類的構(gòu)造函數(shù)的使用, JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); ,調(diào)用默認(rèn)構(gòu)造函數(shù)創(chuàng)建StringBuffer對(duì)象buffer1,調(diào)用指定初始容量的構(gòu)造函數(shù)創(chuàng)建StringBuffer對(duì)象buffer2,調(diào)用指

28、定初始字符串的構(gòu)造函數(shù)創(chuàng)建StringBuffer對(duì)象buffer3,7.3.2 StringBuffer類的方法,表7-4 StringBuffer類的常用方法,7.3.2 StringBuffer類的方法（續(xù)）,7.3.2 StringBuffer類的方法（續(xù)）,7.3.2 StringBuffer類的方法（續(xù)）,7.3.2 StringBuffer類的方法（續(xù)）,例7-7StringBuffer類的append方法的使用 StringBuffer類提供11個(gè)重載的append方法，以允許將各種類型的值添加到StringBuffer對(duì)象的末尾。 11個(gè)重載的append方法方法可以處理各種

29、基本類型數(shù)據(jù)、字符數(shù)組、String對(duì)象、Object對(duì)象和StringBuffer對(duì)象。每個(gè)append都接收一個(gè)參數(shù)，并將該參數(shù)轉(zhuǎn)換為一個(gè)字符串，然后將該字符串添加到StringBuffer對(duì)象的末尾。,7.3.2 StringBuffer類的方法（續(xù)）,7.3.2 StringBuffer類的方法（續(xù)）,/StringBufferAppend.java import javax.swing.*; public class StringBufferAppend public static void main( String args ) Object objectRef = hello;

30、String string = goodbye; char charArray = a, b, c, d, e, f ; boolean booleanValue = true; char characterValue = Z; int integerValue = 7; long longValue = 10000000; float floatValue = 2.5f; double doubleValue = 33.333;,7.3.2 StringBuffer類的方法（續(xù)）,StringBuffer lastBuffer = new StringBuffer( last StringB

31、uffer ); StringBuffer buffer = new StringBuffer(); buffer.append( objectRef ); buffer.append( ); buffer.append( string ); buffer.append( ); buffer.append( charArray ); buffer.append( ); buffer.append( charArray, 0, 3 ); buffer.append( ); buffer.append( booleanValue ); buffer.append( ); buffer.append

32、( characterValue ); buffer.append( ); buffer.append( integerValue ); buffer.append( );,添加Object類型的值,添加兩個(gè)空格作為分割,添加String類型的值,添加字符數(shù)組類型的值,添加字符數(shù)組中的子字符串,添加boolean類型的值,添加char類型的值,添加int類型的值,7.3.2 StringBuffer類的方法（續(xù)）,buffer.append( longValue ); buffer.append( ); buffer.append( floatValue ); buffer.append( )

33、; buffer.append( doubleValue ); buffer.append( ); buffer.append( lastBuffer ); JOptionPane.showMessageDialog( null, buffer = + buffer.toString(), StringBuffer類的append方法的使用, JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); ,添加long類型的值,添加float類型的值,添加double類型的值,添加StringBuffer類型的值,例7-8 StringBuffer類

34、的插入和刪除方法使用 StringBuffer類提供10個(gè)重載的insert方法，以允許在StringBuffer對(duì)象的任何位置插入各種類型的值。這些方法可以處理各種數(shù)據(jù)類型、字符數(shù)組、String對(duì)象和Object對(duì)象。 每個(gè)insert方法都能將它的第二個(gè)參數(shù)轉(zhuǎn)換為一個(gè)字符串，并將該字符串插入到第一個(gè)參數(shù)所指定的索引的前面。 StringBuffer類還提供delete和deleteCharAt方法，用于刪除StringBuffer對(duì)象的任何位置上的字符。,7.3.2 StringBuffer類的方法（續(xù)）,7.3.2 StringBuffer類的方法（續(xù)）,/StringBufferIn

35、sert.java import javax.swing.*; public class StringBufferInsert public static void main( String args ) Object objectRef = hello; String string = goodbye; char charArray = a, b, c, d, e, f ; boolean booleanValue = true; char characterValue = K; int integerValue = 7; long longValue = 10000000; float f

36、loatValue = 2.5f; double doubleValue = 33.333;,7.3.2 StringBuffer類的方法（續(xù)）,StringBuffer buffer = new StringBuffer(); buffer.insert( 0, objectRef ); buffer.insert( 0, ); buffer.insert( 0, string ); buffer.insert( 0, ); buffer.insert( 0, charArray ); buffer.insert( 0, ); buffer.insert( 0, charArray, 3,

37、3 ); buffer.insert( 0, ); buffer.insert( 0, booleanValue ); buffer.insert( 0, ); buffer.insert( 0, characterValue ); buffer.insert( 0, ); buffer.insert( 0, integerValue ); buffer.insert( 0, );,插入Object類型的值,插入兩個(gè)空格作為分割,插入String類型的值,插入字符數(shù)組類型的值,插入字符數(shù)組中的子字符串,插入boolean類型的值,插入char類型的值,插入int類型的值,7.3.2 Strin

38、gBuffer類的方法（續(xù)）,buffer.insert( 0, longValue ); buffer.insert( 0, ); buffer.insert( 0, floatValue ); buffer.insert( 0, ); buffer.insert( 0, doubleValue ); String output = buffer after inserts:n + buffer.toString(); buffer.deleteCharAt( 10 ); buffer.delete( 2, 6 ); output += nnbuffer after deletes:n +

39、buffer.toString(); JOptionPane.showMessageDialog( null, output, StringBuffer類的插入和刪除方法使用, JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); ,插入long類型的值,插入float類型的值,插入double類型的值,刪除2.5中的5,刪除33.333中的.333,7.4 StringTokenizer類,我們?cè)陂喿x一句話時(shí)，常常會(huì)在腦海里將這句話分解為語言詞匯（token）：獨(dú)立的單詞和標(biāo)點(diǎn)符號(hào). 語句單詞之間由定界符分開:空格、制表符、換行符和回車符等

40、 StringTokenizer類位于java.util包,The following is one example of the use of the tokenizer. The code: StringTokenizer st = new StringTokenizer(this is a test); while (st.hasMoreTokens() println(st.nextToken(); prints the following output: this is a test,7.4 StringTokenizer類 （續(xù)）,表7-5 StringTokenizer類的構(gòu)造函

41、數(shù),7.4 StringTokenizer類 （續(xù)）,表7-6 StringTokenizer類的常用方法,/TokenExample.java import java.util.*; class TokenExample public static void main( String args ) String s = This%is!the$way#theworld%ends; String delimiters = !%$#; StringTokenizer st = new StringTokenizer( s, delimiters ); while ( st.hasMoreToke

42、ns() ) System.out.println( st.nextToken() ); ,This The Way The World ends,例7-9 StringTokenizer類的使用 說明StringTokenizer類的使用。該例子顯示一個(gè)窗口，在窗口的一個(gè)JTextField中輸入要一個(gè)語句，按回車后，程序?qū)⒎?hào)化的結(jié)果顯示在窗口的JTextArea中。,7.4 StringTokenizer類 （續(xù)）,7.4 StringTokenizer類 （續(xù)）,/TokenTest.java import java.util.*; import java.awt.*; import

43、java.awt.event.*; import javax.swing.*; public class TokenTest extends JFrame private JLabel promptLabel; private JTextField inputField; private JTextArea outputArea; public TokenTest() super( 測(cè)試StringTokenizer類 ); Container container = getContentPane(); container.setLayout( new FlowLayout() ); prom

44、ptLabel = new JLabel( 輸入一個(gè)句子，然后按回車 ); container.add( promptLabel ); inputField = new JTextField( 20 );,7.4 StringTokenizer類 （續(xù)）,inputField.addActionListener( new ActionListener() public void actionPerformed( ActionEvent event ) StringTokenizer tokens = new StringTokenizer( event.getActionCommand() )

45、; outputArea.setText( Number of elements: + tokens.countTokens() + nThe tokens are:n ); while ( tokens.hasMoreTokens() ) outputArea.append( tokens.nextToken() + n ); );,調(diào)用StringTokenizer構(gòu)造函數(shù)以JTextField字段中的字符串（event.getActionCommand()）建立對(duì)象tokens,調(diào)用StringTokenizer類的方法countTokens,調(diào)用StringTokenizer類的方法h

46、asMoreTokens方法,調(diào)用StringTokenizer類的方法nextToken方法,7.4 StringTokenizer類 （續(xù)）,container.add( inputField ); outputArea = new JTextArea( 10, 20 ); outputArea.setEditable( false ); container.add( new JScrollPane( outputArea ) ); setSize( 275, 240 ); setVisible( true ); public static void main( String args )

47、 TokenTest application = new TokenTest(); application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE ); ,7.5 Vector類,在Java，數(shù)組的存儲(chǔ)空間大小是固定的：它們不能隨應(yīng)用程序的存儲(chǔ)需求的變化而變大或縮小。 Java.util包中的Vector類提供類似于數(shù)組的能力，但能夠動(dòng)態(tài)地調(diào)整自身存儲(chǔ)空間的大小。 Vector（向量）類似于一個(gè)數(shù)組，但與數(shù)組相比在使用上有以下兩個(gè)優(yōu)點(diǎn)： （1）使用的時(shí)候無需聲明上限，隨著元素的增加，Vector的長度會(huì)自動(dòng)增加。 （2）Vector提供額外

48、的方法來增加、刪除元素，比數(shù)組操作高效。,The difference between array and vector,Arrays Related data items of same type Primitive type Reference type Remain same size once created Fixed-length Vectors : java.util Similar to Arrays Dynamically resizable the number of elements can been changed while your code is executin

49、g Related data items of same type Only reference type, not primitive type -Wrapper classes,Vector class constructor,import java.util.*; /Constructs an empty vector with an array size of 10 and a capacity increment of zero Vector aVector=new Vector(); Each vector tries to optimize storage management

50、by maintaining a capacity and a capacityIncrement. capacity -the length of its internal data array capacityIncrement - the amount by which the capacity is increased when the vector overflows If the capacity increment is less than or equal to zero, the capacity of the vector is doubled each time it n

51、eeds to grow. size - the number of components in this vector,7.5 Vector類 （續(xù)）,表7-7 Vector類的構(gòu)造函數(shù),表7-8 Vector類中的常用方法,7.5 Vector類 （續(xù)）,例7-10 Vector類的使用 下面通過例子說明Vector類的使用。,7.5 Vector類 （續(xù)）,7.5 Vector類 （續(xù)）,/VectorTest.java import java.util.*; public class VectorTest private static final String colors = red

52、, white, blue ; public VectorTest() Vector vector = new Vector(); printVector( vector ); vector.add( magenta ); for ( int count = 0; count colors.length; count+ ) vector.add( colors count ); vector.add( cyan ); printVector( vector );,建立VectorTest類的構(gòu)造函數(shù),調(diào)用Vector類的默認(rèn)構(gòu)造函數(shù),調(diào)用printVector方法,調(diào)用Vector類的add方

53、法,7.5 Vector類 （續(xù)）,try System.out.println( First element: + vector.firstElement() ); System.out.println( Last element: + vector.lastElement() ); catch ( NoSuchElementException exception ) exception.printStackTrace(); if ( vector.contains( red ) ) System.out.println( red found at index + vector.indexO

54、f( red ) ); else System.out.println( red not foundn ); vector.remove( red );,調(diào)用Vector類的firstElement方法,調(diào)用Vector類的lastElement方法,調(diào)用Vector類的contains方法,調(diào)用Vector類的indexOf方法,調(diào)用Vector類的remove方法,7.5 Vector類 （續(xù)）,System.out.println( red has been removed ); printVector( vector ); if ( vector.contains( red ) ) S

55、ystem.out.println( red found at index + vector.indexOf( red ) ); else System.out.println( red not found ); System.out.println( Size: + vector.size() + nCapacity: + vector.capacity() ); ,調(diào)用Vector類的size和capacity方法,7.5 Vector類 （續(xù)）,private void printVector( Vector vectorToOutput ) if ( vectorToOutput.isEmpty() ) System.out.print( vector is empty ); else System.out.print( vector cont