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@Sarah 2015-11-05T17:52:28.000000Z 字数 9714 阅读 966

JAVA 数组 String 异常

java笔记
构造函数可以用右键source自动写，还有toString（）

string

常用函数

求字符串长度：.length()

求数组长度：

  1. int i[]=new int[100]
  2. i.length

去掉首尾空格： .trim()

" abc d \t\n ".trim()
返回abc d“”

大小写：

toLower()
toUpper()

例

  1. strung s="4ABC";
  2. s=s.tolower();
  3. //后面一定要把值赋给一个变量 否则会被回收

转换成char:

  1. s="4abc"
  2. char c[];
  3. c=s.getChars();
  4. //c=“4” "a" "b" "c"
  5. c.length  //=4
  6. s.length // =4

indexOf()

  1. "abcabc"
  2. indexOf("c") //2
  3. indexOf("ca") //2
  4. indexOf("ac") //-1
  5. indexOf("a")  //0
  7. indexOf("ab,2") //3 从第二个开始往后找“ab”
  9. LastIndexOf()
  1. 这个例子没看懂呢= =
  2. int [] i=new int [10];
  3. Point p=new Point();
  4. Point ps[]=new Point[30];//p[0].x=0 ,p[0]= new Point
  5. for(int j=0;j<30;j++)
  6.     ps[j]=new Point();
  7. P[0].x=0;

StringBuffer

  1. （String args[]）
  2. char c='A'; //char不能有两个字母”AB“
  3. String  s=new String("ABC");
  4.     s="ABC";
  5. String t;
  6.     t="DEF"
  7.     s=s+"DEF";//此时变成ABCDEF !这里到底能不能加？？！！
  8.     //不可变字符串
  9. StringBuffer m=new StringBuffer("ABC");

.SubString()

  1. "ABCDEF".SubString(2,4)
  2. //"CD"  4-2=α 从第二个开始数到第四个之前

.CompareTo()

  1. "ABC".CompareTo("AB")
  2. //1
  3. //前面>后面 1
  4. //前面=后面 0
  5. //前面<后面 -1

.concat()

  1. s="ABC".concat("DEF")
  2.     ///"ABC"+"DEF"---"ABCDEF"
  3.     //A=65 汉字在两万左右

异常

  1. try{
  2.             //这里写可能产生的异常 相关 对象
  3.     }
  4. catch(对象){
  5.             //引用上面try里的对象
  6.     }
  7. catch(对象){
  8.              //引用上面try里的对象
  9.     }

finally:无论如何都会执行

数组例子

  1. Matrix{
  2.     int data[][];
  3.     Matrix(int rows,int cols){
  4.         if(rows>0 &&cols>0)
  5.             data=new int[rows][cols];
  6.         else
  7.             throw new Exception("XXXXX")
  8.         }
  9.     }
  1. //数组test
  2.     i=m.getData(1,1);
  3.     t=m.multiply(n)
  1. 数组相乘
  2.       Matrix result=new Matrix(rows,n.getCols());
  3.             for(i=0;i<rows;i++)
  4.                 for(j=0;j<n.getCols();j++)      
  5.                     for(k=0;k<cols;k++)
  6.                             result.setData(i,j,result.getData(i,j)+data[i][k]*n.getData(k,j));
  8.         return result;

J2SE:
1语句 数据类型关键字
2面向对象：类 对象 包 三种特性
object ,static , final
抽象类，接口
3数组：string,异常
4I/o,线程，网络，gui，java.swing

两个方向
j2ee w=网站 html css
andriod 应用

第一个大案例

  1. public class Circle {
  2.     Point center;
  3.     int radius;
  4.     public Circle(Point center, int radius) throws Exception {//声明抛出异常
  5.         if (center!=null && radius>=0){
  6.             this.center = center;
  7.             this.radius = radius;
  8.         }
  9.         else {
  10.             Exception e=new MyException();
  11.             throw e;//抛出异常
  12.         }
  13.     }
  14.     public static void main(String[] args) {
  15.         Point p=null;
  16.         Circle c=null;
  17.         try {
  18.             c=new Circle(p, 5);
  19.         } catch (Exception e) {
  20.             // TODO Auto-generated catch block
  21.             System.out.println(e);
  22.             //javax.swing.JOptionPane.showMessageDialog(null,e);
  23.         }
  24.     }
  25. }
  1. public class MyException extends Exception {
  3.     @Override
  4.     public String toString() {
  5.         return "参数错误!";
  6.     }
  8. }
  2. public class Point {
  3.     int x,y;
  5.     public Point(int x, int y) {
  6.         super();
  7.         this.x = x;
  8.         this.y = y;
  9.     }
  11.     @Override
  12.     public String toString() {
  13.         return "Point [x=" + x + ", y=" + y + "]";
  14.     }
  16. }

第二个例子

  1. public class Test {
  2.     public static void main(String[] args) {
  3.         String c="汉字";
  4.         byte[] b=c.getBytes();
  5.         char[] cc=new char[c.length()];
  6.         c.getChars(0,c.length(),cc,0);
  7.         int i=(int)(Math.random()*30);
  8.         try{
  9.             double d=10/i;
  10.             System.out.println(d);
  11.             for( i=0;i<=cc.length;i++)
  12.                 System.out.println((int)cc[i]);
  13.         }
  14.         catch(ArithmeticException ex){
  15.             System.out.println(ex);
  16.         }
  17.         catch(ArrayIndexOutOfBoundsException ex){
  18.             System.out.println("--------"+ex);
  19.             return;
  20.         }
  21.         finally{
  22.             System.out.println("123456789");
  23.         }
  24.         System.out.println((char) 25721);
  25.         System.out.println("done.");
  26.     }
  28.     public static void main1(String[] args) {
  29.         // TODO Auto-generated method stub
  30.         String s;
  31.         StringBuffer t=new StringBuffer("");
  32.         char c=65;
  33.         System.out.println(c);
  34.         int i=0;
  35.         for(;i<2000;i++){
  36.             t.append( (char) ((int)(Math.random()*26+65)) );
  37.         }
  38.         s=t.toString();
  39.         i=0;
  40.         System.out.println(s);
  41.         while(true){
  42.             int pos=s.indexOf("YU",i);
  43.             if(pos<0)
  44.                 break;
  45.             System.out.println(pos);
  46.             i=pos+1;
  47.         }
  48. //      s.g
  49.         System.out.println(s.lastIndexOf("YU",1700));
  50.     }
  52. }

第三个例子（略）

  1. class WordDictionary{
  2.    private final int dictionaryLength=157;
  3.    private int index=-1;
  4.    private String[] words={
  5.       "ability","able","aboard","about","above",
  6.       "abroad","absence","absent","absolute","absorb",
  7.       "abstract","abundant","abuse","academic","academy",
  8.       "accelerate","accent","accept","acceptance","access",
  9.       "accident","accidental","accommodation","accompany","accomplish",
  10.       "accord","accordance","accordingly","account","accountant",
  11.       "accumulate","accuracy","accurate","accuse","accustomed",
  12.       "ache","achieve","achievement","acid","acknowledge",
  13.       "acquaintance","acquire","acquisition","acre","across",
  14.       "action","active","activity","actor","actress",
  15.       "actual","acute","adapt","addition","additional",
  16.       "address","adequate","adjective","adjust","administration",
  17.       "admire","admission","admit","adopt","adult",
  18.       "advance","advanced","advantage","adventure","adverb",
  19.       "advertise","advertisement","advice","advisable","advise",
  20.       "advocate","aeroplane","affair","affect","affection",
  21.       "afford","afraid","after","afternoon","again",
  22.       "agency","agenda","agent","aggressive","agree",
  23.       "agreement","agriculture","ahead","aircraft","airline",
  24.       "airplane","against","airport","alarm","alcohol",
  25.       "alert","alike","alive","all","alliance",
  26.       "allocate","allow","allowance","ally","almost",
  27.       "alone","along","alongside","aloud","alphabet",
  28.       "already","also","alter","alternative","although",
  29.       "altitude","altogether","aluminium","aluminum","always",
  30.       "amateur","amaze","ambassador","ambition","ambulance",
  31.       "amid","among","amongst","amount","amuse",
  32.       "analyse","analysis","analyze","ancestor","anchor",
  33.       "ancient","and","anger","angle","angry",
  34.       "animal","ankle","anniversary","announce","annoy",
  35.       "annual","another","answer","anticipate","antique",
  36.       "anxiety","anxious"};
  37.    public String getMagicWord(){
  38.       int i=(int)(Math.random()*dictionaryLength);
  39.       index=i;
  40.       return convertWord(words[i]);
  41.    }   
  42.    private String convertWord(String word){
  43.       char[] charsInWord=word.toCharArray();
  44.       for(int i=charsInWord.length-1; i>0; i--)
  45.           for(int j=0; j<i; j++)
  46.               if  ( charsInWord[ j ] > charsInWord[ j+1 ] ){
  47.                   char temp=charsInWord[ j ];
  48.                   charsInWord[ j ]=charsInWord[ j+1 ];
  49.                   charsInWord[ j+1 ]=temp;
  50.               }      
  51.       return new String(charsInWord);
  52.    }
  53.    public String getOriginalWord(){
  54.       return words[index];
  55.    }
  56. }
  58. class GuessWord{
  59.    public static void main(String args[]){
  60.       WordDictionary wd=new WordDictionary();
  61.       int guessTimes=0,correctTimes=0;
  62.       while(true){
  63.          System.out.println("猜猜这是什么单词:"+wd.getMagicWord());
  64.          guessTimes++;
  65.          if(wd.getOriginalWord().equals(KeyInput.readString())){
  66.             System.out.println("对了，就是 "+wd.getOriginalWord());
  67.             correctTimes++;
  68.          }
  69.          else
  70.             System.out.println("错了，是 "+wd.getOriginalWord()); 
  71.          System.out.print("继续玩吗？(y/n)");
  72.          if(KeyInput.readString().toLowerCase().equals("n")) 
  73.             break;
  74.          }
  75.       System.out.println("猜对率为"+(correctTimes*100/guessTimes)+"%,拜拜喽...");
  76.    }
  77. }
  1. import java.io.*;
  3. public class KeyInput {
  4.     static InputStreamReader isr = new InputStreamReader(System.in);
  5.     static BufferedReader br = new BufferedReader(isr);
  7.     public static int readInt() {
  8.         int i = 0;
  9.         try {
  10.             i = Integer.parseInt(readString());
  11.         } catch (Exception e) {
  12.             System.out.println(e);
  13.         }
  14.         return i;
  15.     }
  17.     public static float readFloat() {
  18.         float f = 0.0f;
  19.         try {
  20.             f = Float.parseFloat(readString());
  21.         } catch (Exception e) {
  22.             System.out.println(e);
  23.         }
  24.         return f;
  25.     }
  27.     public static double readDouble() {
  28.         double d = 0.0;
  29.         try {
  30.             d = Double.parseDouble(readString());
  31.         } catch (Exception e) {
  32.             System.out.println(e);
  33.         }
  34.         return d;
  35.     }
  37.     public static String readString() {
  38.         String s = "";
  39.         try {
  40.             s = br.readLine();
  41.             if (s.length() == 0)
  42.                 s = br.readLine();
  43.         } catch (Exception e) {
  44.             System.out.println(e);
  45.         }
  46.         return s;
  47.     }
  49.     public static boolean readBoolean() {
  50.         if (readString().toUpperCase().equals("TRUE"))
  51.             return true;
  52.         else
  53.             return false;
  54.     }
  56.     public static char readChar() {
  57.         try {
  58.             return readString().charAt(0);
  59.         } catch (Exception e) {
  60.             System.out.println(e);
  61.         }
  62.         return ' ';
  63.     }
  65.     public static void main(String args[]) {
  67.         System.out.print("Please input an integer number:");
  68.         System.out.println("Your input is " + KeyInput.readInt());
  69.         System.out.print("Please input a float number:");
  70.         System.out.println("Your input is " + KeyInput.readFloat());
  71.         System.out.print("Please input a double number:");
  72.         System.out.println("Your input is " + KeyInput.readDouble());
  73.         System.out.print("Please input a string:");
  74.         System.out.println("Your input is " + KeyInput.readString());
  75.         System.out.print("Please input a boolean value:");
  76.         System.out.println("Your input is " + KeyInput.readBoolean());
  77.         System.out.print("Please input a char:");
  78.         System.out.println("Your input is " + KeyInput.readChar());
  80.     }
  81. }

大作业Matrix

  1. public class IllegalArgumentException extends Exception {
  3.     @Override
  4.     public String toString() {
  5.         return "矩阵行数或列数非法";
  6.     }
  8. }

public class IllegalIndexException extends Exception{

@Override
public String toString() {
    return "矩阵行号或列号非法";
}

}

  2. public class Matrix {
  3.     int rows;
  4.     int cols;
  5.     double data[][];
  7.     private Matrix() {
  8.     }
  10.     public Matrix(int rows, int cols) throws IllegalArgumentException {
  11.         super();
  12.         if (rows >= 1 && cols >= 1) {
  13.             this.rows = rows;
  14.             this.cols = cols;
  15.             this.data = new double[rows][cols];
  16.         } else {
  17.             //Exception e = new IllegalArgumentException();
  18.             throw new IllegalArgumentException();
  19.         }
  21.     }
  23.     public Matrix(int rows, int cols, double[][] data) throws IllegalArgumentException {
  24.         super();
  25.         if (rows >= 1 && cols >= 1) {
  26.             this.rows = rows;
  27.             this.cols = cols;
  28.             this.data = data;
  29.         } else {
  30.             //Exception e = new IllegalArgumentException();
  31.             throw new IllegalArgumentException();
  32.         }
  34.     }
  36.     public double getData(int rows, int cols) throws IllegalIndexException {
  37.         if (this.cols > cols && this.rows > rows) {
  38.             return data[rows][cols];
  39.         } else {
  40.             //Exception f = new IllegalIndexException();
  41.             throw new IllegalIndexException();
  42.         }
  43.     }
  45.     public void setData(int rows, int cols, double value) throws IllegalIndexException {
  46.         if (this.cols > cols && this.rows > rows) {
  47.             this.data[rows][cols] = value;
  48.             // return data[rows][cols];
  49.         } else {
  50.             //Exception f = new IllegalIndexException();
  51.             throw new IllegalIndexException();
  52.         }
  53.     }
  55.     public Matrix multiply(Matrix m) throws MatrixMultiplicationException,
  56.             IllegalIndexException,IllegalArgumentException{
  57.         if (cols == m.rows) {
  58.             Matrix result = new Matrix(rows, m.cols);
  59.             int i, j, k;
  60.             for (i = 0; i < rows; i++)
  61.                 for (j = 0; j < m.cols; j++)
  62.                     for (k = 0; k < cols; k++)
  63.                         result.setData(i, j, result.getData(i, j) + data[i][k]
  64.                                 * m.getData(k, j));
  65.             return result;
  66.         } else {
  67.         //  Exception g = new MatrixMultiplicationException();
  68.             throw new MatrixMultiplicationException();
  69.         }
  70.     }
  72.     public String toString() {
  73.         StringBuffer s = new StringBuffer("");
  74.         for (int i = 0; i < rows; i++) {
  75.             s.append("[");
  76.             for (int j = 0; j < cols; j++) {
  77.                 s.append(data[i][j]);
  78.                 if (j + 1 != cols)
  79.                     s.append("\t");
  80.             }
  81.             s.append("]\n");
  82.         }
  83.         return s.toString();
  85.     }
  86. }
  2. public class MatrixMultiplicationException extends Exception {
  4.     @Override
  5.     public String toString() {
  6.         return "矩阵无法相乘异常";
  8.     }
  10. }
  1. public class MatrixTest {
  3.     public static void main(String[] args)  {
  4.         try {
  5.             Matrix m = new Matrix(1, 7);
  6.             Matrix n = new Matrix(7, 5);
  7.             for (int i = 0; i < m.rows; i++)
  8.                 for (int j = 0; j < m.cols; j++)
  9.                     m.setData(i, j, (int) (Math.random() * 10));
  10.             for (int i = 0; i < n.rows; i++)
  11.                 for (int j = 0; j < n.cols; j++)
  12.                     n.setData(i, j, (int) (Math.random() * 10));
  13.             Matrix r = m.multiply(n);
  14.             System.out.println(m);
  15.             System.out.println(n);
  16.             System.out.println(r);
  17.         } catch (IllegalArgumentException e) {
  18.             System.out.println(e);
  19.         } catch (IllegalIndexException f) {
  20.             System.out.println(f);
  21.         } catch (MatrixMultiplicationException g) {
  22.             System.out.println(g);
  23.         }
  24.         catch(Exception e){
  25.             System.out.println(e);
  26.         }
  27.     }
  28. }
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