基本概念6-声明数组和给数组分配内存6-数组汇总课件

1、6.1 基本概念6.2 声明数组和给数组分配内存6.3 数组应用举例6.4 把数组传递给方法6.5 多维数组6.1 基本概念6.1 基本概念 数组是由同一类型的相关数据构成的有序数据集合，根据数组名和下标来唯一地确定数组中的元素。 数组是静态实体，一旦被创建，其大小保持不变，但是数组引用可以重新赋值为不同大小的数组。 在Java中规定，数组的第一个元素的下标为。 在Java中，每一个数组知道自己的长度，由一个称为length的变量存储。如：数组arr的长度表示为arr.length。6.1 基本概念6.2 声明数组和给数组分配内存在Java中，所有的对象(包括数组)必须由new操作符动态分配内

2、存。对数组而言，编程人员所指定的数组元素的类型和元素的数目是new操作符的一部分。例如，声明一个长度为12的整型数组c，并为其分配内存，可以使用下面的语句：int c = new int12;也可以将声明数组和分配内存分开进行：int c; / declares the array c = new int12; / allocates the array给数组分配内存之后，基本数据类型数值的数组元素将会被赋默认值为，布尔型(boolean)数组的默认值为假(false)，对于非基本类型的数组引用，则赋予值为空(null)。可以通过一条声明语句为多个数组分配内存空间，如：String b=new

3、 String50,x=new String27;数组的类型和方括号可以在声明的开始处结合起来使用，表示声明中的所有标识符都是数组。double arr1,arr2; arr1=new double20; arr2=new double40;6.2 声明数组和给数组分配内存6.3 数组应用举例例6.1 分配数组内存并初始化数组元素。/ Fig. 7.3: InitArray.javaimport javax.swing.*;public class InitArray public static void main( String args ) int array; / declare ref

4、erence to an array array = new int 10 ; / dynamically allocate array String output = SubscripttValuen; for ( int counter = 0; counter array.length; counter+ ) output += counter + t + array counter + n; JTextArea outputArea = new JTextArea(); outputArea.setText( output ); JOptionPane.showMessageDialo

5、g( null, outputArea, Initializing an Array of int Values, JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); 6.3 数组应用举例例6.2 用初值表对数组进行初始化。/ Fig. 7.4: InitArray.javaimport javax.swing.*;public class InitArray public static void main( String args ) int array = 32, 27, 64, 18, 95, 14, 90, 70, 60, 37 ;

6、 String output = SubscripttValuen; for ( int counter = 0; counter array.length; counter+ ) output += counter + t + array counter + n; JTextArea outputArea = new JTextArea(); outputArea.setText( output ); JOptionPane.showMessageDialog( null, outputArea, Initializing an Array with a Declaration, JOpti

7、onPane.INFORMATION_MESSAGE ); System.exit( 0 ); 例6.2 用初值表对数组进行初始化。例6.3 计算并存储数组元素的值。/ Fig. 7.5: InitArray.javaimport javax.swing.*;public class InitArray public static void main( String args ) final int ARRAY_SIZE = 10; int array; / reference to int array array = new int ARRAY_SIZE ; / allocate array

8、 for ( int counter = 0; counter array.length; counter+ ) array counter = 2 + 2 * counter; String output = SubscripttValuen; for ( int counter = 0; counter array.length; counter+ ) output += counter + t + array counter + n; JTextArea outputArea = new JTextArea(); outputArea.setText( output ); JOption

9、Pane.showMessageDialog( null, outputArea, Initializing to Even Numbers from 2 to 20, JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); 例6.3 计算并存储数组元素的值。例6.4 使用柱状图显示数组数据。/ Fig. 7.7: Histogram.javaimport javax.swing.*;public class Histogram public static void main( String args ) int array = 19, 3,

10、15, 7, 11, 9, 13, 5, 17, 1 ; String output = ElementtValuetHistogram; for ( int counter = 0; counter array.length; counter+ ) output += n + counter + t + array counter + t; for ( int stars = 0; stars array counter ; stars+ ) output += *; JTextArea outputArea = new JTextArea(); outputArea.setText( ou

11、tput ); JOptionPane.showMessageDialog( null, outputArea, Histogram Printing Program, JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); 例6.4 使用柱状图显示数组数据。例6.5 使用数组元素作为计数器统计掷骰子6000次的情况。/ Fig. 7.8: RollDie.javaimport javax.swing.*;public class RollDie public static void main( String args ) int face,

12、frequency = new int 7 ; for ( int roll = 1; roll = 6000; roll+ ) face = 1 + ( int ) ( Math.random() * 6 ); +frequency face ; String output = FacetFrequency; for ( face = 1; face frequency.length; face+ ) output += n + face + t + frequency face ; JTextArea outputArea = new JTextArea(); outputArea.set

13、Text( output ); JOptionPane.showMessageDialog( null, outputArea, Rolling a Die 6000 Times, JOptionPane.INFORMATION_MESSAGE ); System.exit( 0 ); 例6.5 使用数组元素作为计数器统计掷骰子6000次的情况6.4 把数组传递给方法把数组传递给一个方法，应使用不加方括号的数组名。例6.6 把数组和单个元素传递给方法。/ Fig. 7.10: PassArray.javaimport java.awt.Container;import javax.swing.

14、*;public class PassArray extends JApplet public void init() JTextArea outputArea = new JTextArea(); Container container = getContentPane(); container.add( outputArea ); int array = 1, 2, 3, 4, 5 ; String output = Effects of passing entire array by reference:n + The values of the original array are:n

15、; for ( int counter = 0; counter array.length; counter+ ) output += + array counter ; modifyArray( array ); output += nnThe values of the modified array are:n; for ( int counter = 0; counter array.length; counter+ ) output += + array counter ; output += nnEffects of passing array + element by value:

16、n + array3 before modifyElement: + array 3 ; modifyElement( array 3 ); output += narray3 after modifyElement: + array 3 ; outputArea.setText( output ); / end method init6.4 把数组传递给方法 public void modifyArray( int array2 ) for ( int counter = 0; counter array2.length; counter+ ) array2 counter *= 2; pu

17、blic void modifyElement( int element ) element *= 2; / end class PassArray public void modifyArray( in例6.7 数组排序。/ Fig. 7.11: BubbleSort.javaimport java.awt.*;import javax.swing.*;public class BubbleSort extends JApplet public void init() JTextArea outputArea = new JTextArea(); Container container =

18、getContentPane(); container.add( outputArea ); int array = 2, 6, 4, 8, 10, 12, 89, 68, 45, 37 ; String output = Data items in original ordern; for ( int counter = 0; counter array.length; counter+ ) output += + array counter ; bubbleSort( array ); / sort array output += nnData items in ascending ord

19、ern; for ( int counter = 0; counter array.length; counter+ ) output += + array counter ; outputArea.setText( output ); 例6.7 数组排序。 public void bubbleSort( int array2 ) for ( int pass = 1; pass array2.length; pass+ ) for ( int element = 0; element array2 element + 1 ) swap( array2, element, element +

20、1 ); / end loop to control comparisons / end loop to control passes / end method bubbleSort public void swap( int array3, int first, int second ) int hold; / temporary holding area for swap hold = array3 first ; array3 first = array3 second ; array3 second = hold; / end class BubbleSort public void

21、bubbleSort( int6.5 多维数组例6.8 采用applet统计学生成绩情况(每个学生有4门课程成绩)。/ Fig. 7.16: DoubleArray.javaimport java.awt.*;import javax.swing.*;public class DoubleArray extends JApplet int grades = 77, 68, 86, 73 , 96, 87, 89, 81 , 70, 90, 86, 81 ; int students, exams; String output; JTextArea outputArea; public void

22、 init() students = grades.length; / number of students exams = grades 0 .length; / number of exams outputArea = new JTextArea(); Container container = getContentPane(); container.add( outputArea ); output = The array is:n; buildString(); output += nnLowest grade: + minimum() + nHighest grade: + maxi

23、mum() + n; for ( int counter = 0; counter students; counter+ ) output += nAverage for student + counter + is + average( grades counter ); outputArea.setFont( new Font( Courier, Font.PLAIN, 12 ) ); outputArea.setText( output ); 6.5 多维数组 public int minimum() int lowGrade = grades 0 0 ; for ( int row = 0; row students; row+ ) for ( int column = 0; column exams; column+ ) if ( grades row column lowGrade ) lowGrade = grad