Jse练习题目及答案

1、1 Java初学者第一个小程序public class HelloWorld public static void main(String args) System.out.println("Hello World!");2 break练习public class TestBreak public static void main(String args) int stop = 4;for(int i=1; i<=10; i+) if(i = stop) break; else System.out.println(i);3 continue练习public clas

2、s TestContinute public static void main(String args) int con = 3;for(int i=1; i<=5; i+) if(i = con) continue; else System.out.println(i);4 使用非递归的方法求Fibonacci数列第5个数是多少? /1, 1, 2, 3, 5, 8, 13public class TestFab public static void main(String args) System.out.println(method(5);public static long me

3、thod(int index) if(index = 1 | index = 2) return 1;long f1 = 1L;long f2 = 1L;long f = 0;for(int i=0; i<index-2; i+) f = f1 + f2;f1 = f2;f2 = f;return f;5 使用递归求Fibonacci数列第5个数是多少?答:5public class TestFibonacci public static void main(String args) System.out.println(method(5);public static int metho

4、d(int n) if(n = 1 | n = 2) return 1; else return method(n - 1) + method(n - 2);6 使用for循环求1! + 2! + 3! + . + 10! = 4037913;public class TestFor1 public static void main(String args) long f = 1L;long result = 0;for(int i=1; i<=10; i+) f *= i;result += f;System.out.println(result);7 使用for循环求1 + 3 +

5、5 + . + 99 = 2500;public class TestFor2 public static void main(String args) int result = 0;for(int i=1; i<=99; i+=2) result += i;System.out.println(result);8 if练习public class TestIF public static void main(String args) int i = 20;if(i<20) System.out.println("i < 20"); else if (i&

6、lt;40) System.out.println("i < 40"); else if(i>60) System.out.println("asf"); else System.out.println("kasjfla");9 使用递归求5! = 120;public class TestJC public static void main(String args) System.out.println(method(5);public static int method(int n) if(n = 1) return

7、1; else return n * method(n - 1);10 方法的调用举例public class TestMethod public static void main(String args) m1();m2(5);m3(4,5);System.out.println(m4(4, 6);public static void m1() /return;System.out.println("OK");public static void m2(int i) if(i<3) return; else System.out.println(i);public

8、static void m3(int i, int j) System.out.println(i + j);public static int m4(int i, int j) return i < j ? i : j;11 switch问题举例，注意穿透现象public class TestSwitch public static void main(String args) int i = 3;switch(i) case 3 :System.out.println("A");break;case 5 :System.out.println("B&qu

9、ot;);break;default:System.out.println("error"); 12 while do while 举例，将1到9输出public class TestWhile public static void main(String args) int i = 1;while(i<=9) System.out.print(i + " ");i+;System.out.println();i = 1;do System.out.print(i + " ");i+; while (i<=9);13 求3

10、维空间两点坐标之间的距离的平方class Point double x;double y;double z;Point(double x, double y, double z) this.x = x;this.y = y;this.z = z;void setX(double x) this.x = x;void setY(double y) this.y = y;void setZ(double z) this.z = z;double getDistance(Point p) return (x - p.x)*(x - p.x) + (y - p.y)*(y - p.y) + (z -

11、p.z)*(z - p.z);public class TestPoint public static void main(String args) Point p1 = new Point(1.0, 2.0, 3.0);Point p2 = new Point(0.0, 0.0, 0.0);System.out.println(p1.getDistance(p2);p1.setY(1.0);System.out.println(p1.getDistance(new Point(1.0, 1.0, 3.0);14 重写equals方法判定两只猫是否相等public class TestEqua

12、ls public static void main(String args) String s1 = "a"String s2 = "a"System.out.println(s1 = s2);System.out.println(s1.equals(s2);String s3 = new String("hello");String s4 = new String("hello");System.out.println(s3 = s4);System.out.println(s3.equals(s4);Cat

13、c1 = new Cat(1, 2, 3);Cat c2 = new Cat(1, 2, 3);System.out.println(c1 = c2);System.out.println(c1.equals(c2); class Cat int color;int weight;int height;Cat(int color, int weight, int height) this.color = color;this.weight = weight;this.height = height;public boolean equals(Object obj) if(obj = null)

14、 return false; else if(obj instanceof Cat) Cat c = (Cat)obj;if(this.color = c.color && this.height = c.height && this.weight = c.weight) return true;return false;15 多态举例package com.dt;public class TestDt public static void main(String args) Cat c = new Cat("catname", "

15、yellow");Dog d = new Dog("dogname", "black");Lady l1 = new Lady("l1", c);Lady l2 = new Lady("l2", d);l1.myPetEnjoy();l2.myPetEnjoy();class Animal private String name;Animal(String name) = name;public void enjoy() System.out.println("动物的叫声.&

16、quot;);class Cat extends Animal private String eyeColor;Cat(String n, String eyeColor) super(n);this.eyeColor = eyeColor;public void enjoy() System.out.println("猫的叫声.");class Dog extends Animal private String furColor;Dog(String n, String furColor) super(n);this.furColor = furColor;public

17、void enjoy() System.out.println("狗的叫声.");class Lady private String name;private Animal pet;Lady(String name, Animal pet) = name;this.pet = pet;public void myPetEnjoy() pet.enjoy();16 冒泡排序public class BubbleSort public static void main(String args) int a = new intargs.length;for(i

18、nt i=0; i<args.length; i+) ai = Integer.parseInt(argsi);print(a);bubbleSort(a);print(a);private static void print(int a) for(int i=0; i<a.length; i+) System.out.print(ai + " ");System.out.println();private static int bubbleSort(int a) for(int i=a.length-1; i>=1; i-) for(int j=0; j

19、<=a.length-2; j+) if(aj > aj+1) int temp = aj;aj = aj+1;aj+1 = temp;return a;17 使用数组数3退1:非面向对象的写法public class Count3Quit public static void main(String args) Boolean arr = new Boolean500;for(int i=0; i<arr.length; i+) arri = true;int leftCount = arr.length;int countNum = 0;int index = 0;whi

20、le(leftCount > 1) if(arrindex = true) countNum +;if(countNum = 3) countNum = 0;arrindex = false;leftCount -;index +;if(index = arr.length) index = 0;for(int i=0; i<arr.length; i+) if(arri = true) System.out.println(i);18 面向对象的数3退1public class Count3Quit2 public static void main(String args) Ki

21、dCircle kc = new KidCircle(500);int countNum = 0;int leftCount = kc.count;Kid k = kc.first;while(leftCount > 1) countNum +;if(countNum = 3) countNum = 0;kc.delete(k);k = k.right;class Kid int id;Kid(int id) this.id = id;Kid left;Kid right;class KidCircle int count = 0;Kid first, last;KidCircle(in

22、t n) for(int i=0; i<n; i+) add();void add() Kid k = new Kid(count);if(count <= 0) first = k;last = k;k.left = k;k.right = k; else last.right = k;k.left = last;k.right = first;first.left = k;last = k;count +;void delete(Kid k) if(count <= 0) return; else if(count = 1) first = last = null; el

23、se k.left.right = k.right;k.right.left = k.left;if(k = first) first = k.right; else if(k = last) last = k.left;count -;19 选择排序public class SelectionSort public static void main(String args) int a = new intargs.length;for(int i=0; i<args.length; i+) ai = Integer.parseInt(argsi);print(a);selectionS

24、ort(a);print(a);private static void print(int a) for(int i=0; i<a.length; i+) System.out.print(ai + " ");System.out.println();private static void selectionSort(int a) int temp, k;for(int i=0; i<a.length; i+) k = i;for(int j=k+1; j<a.length; j+) if(ak > aj) k = j;if(k != i) temp

25、 = ai;ai = ak;ak = temp;20 简单运算器public class TestArgs public static void main(String args) double d1 = Double.parseDouble(args0);double d2 = Double.parseDouble(args2);double d = 0;if(args1.equals("+") d = d1 + d2; else if(args1.equals("-") d = d1 - d2; else if(args1.equals("

26、x") d = d1 * d2; else if(args1.equals("/") d = d1 / d2; else System.out.println("error");System.out.println(d);21 数组拷贝练习public class TestArrayCopy public static void main(String args) int intArray = 1,2,3,4,5,6,7;int intArrayBak = new int3;System.arraycopy(intArray, 0, intAr

27、rayBak, 0, intArray.length);intArray21 = 100;for(int i=0; i<intArray.length; i+) for(int j=0; j<intArrayi.length; j+) System.out.print(intArrayij + " ");System.out.println(); 22 对日期排序public class TestDateSort public static void main(String args) Date days = new Date5;days0 = new Date

28、(2006, 5, 4);days1 = new Date(2006, 7, 4);days2 = new Date(2008, 5, 4);days3 = new Date(2004, 5, 9);days4 = new Date(2004, 5, 4);Date d = new Date(2006, 7, 4);String str = String.valueOf(d);/str = d.toString();bubbleSort(days);for(int i=0; i<days.length; i+) System.out.println(daysi);System.out.p

29、rintln(binarySearch(days, d); public static Date bubbleSort(Date a) int len = a.length; for(int i = len-1;i>=1;i-) for(int j = 0;j<=i-1;j+) if(pare(aj+1) > 0) Date temp = aj; aj=aj+1; aj+1=temp; return a; public static int binarySearch(Date days, Date d) if (days.length=0) return -1;

30、int startPos = 0; int endPos = days.length-1; int m = (startPos + endPos) / 2; while(startPos <= endPos) if(pare(daysm) = 0) return m; if(pare(daysm) > 0) startPos = m + 1; if(pare(daysm) < 0) endPos = m -1; m = (startPos + endPos) / 2; return -1; class Date int year, month, day; Date(int y

31、, int m, int d) year = y; month = m; day = d; public int compare(Date date) return year > date.year ? 1 : year < date.year ? -1 : month > date.month ? 1 : month < date.month ? -1 : day > date.day ? 1 : day < date.day ? -1 : 0; public String toString() return "Year:Month:Day -

32、" + year + "-" + month + "-" + day; 23 二分法查找public class TestSearch public static void main(String args) int a = 1, 3, 6, 8, 9, 10, 12, 18, 20, 34 ;int i = 12;/System.out.println(search(a, i);System.out.println(binarySearch(a, i);public static int search(int a, int num) for(

33、int i=0; i<a.length; i+) if(ai = num) return i;return -1;public static int binarySearch(inta, int num) if (a.length=0) return -1; int startPos = 0; int endPos = a.length-1; int m = (startPos + endPos) / 2; while(startPos <= endPos) if(num = am) return m; if(num > am) startPos = m + 1; if(nu

34、m < am) endPos = m -1; m = (startPos + endPos) / 2; return -1; 24 将字符串String s = "1,2;3,4,5;6,7,8"分解成一个double的二维数组public class ArrayParser public static void main(String args) double d;String s = "1,2;3,4,5;6,7,8"String sFirst = s.split("");d = new doublesFirst.lengt

35、h;for(int i=0; i<sFirst.length; i+) /System.out.println(sFirsti);String sSecond = sFirsti.split(",");di = new doublesSecond.length;for(int j=0; j<sSecond.length; j+) /System.out.println(sSecondj);dij = Double.parseDouble(sSecondj);for(int i=0; i<d.length; i+) for(int j=0; j<di.

36、length; j+) System.out.println(dij);25 列出D:/A下边所以的文件及文件夹import java.io.*;public class FileList public static void main(String args) File f = new File("d:/A");System.out.println(f.getName();tree(f, 1);private static void tree(File f, int level) String str = ""for(int i=0; i<lev

37、el; i+) str += " "File childs = f.listFiles();for(int i=0; i<childs.length; i+) System.out.println(str + childsi.getName();if(childsi.isDirectory() tree(childsi, level + 1);26 枚举举例enum MyColor red3, green, blue;public class TestEnum public static void main(String args) MyColor m = MyCol

38、or.red3;long l1 = 3333333255252553L;int i = (int) l1;System.out.println(i);short s = 5; s = (short) (s + 2); s += 2; switch(m) case red3 :System.out.println(MyColor.red3);break;case green :System.out.println("B_green");break;case blue :System.out.println("C_blue");break;default :

39、System.out.println("error");break;System.out.println(m.toString().intern()="red3");27 创建文件java.txtimport java.io.*;public class TestFile public static void main(String args) String seperator = File.separator;String fileName = "naruto.txt"String directory = "m1/m2&q

40、uot;File f = new File(directory, fileName);if(f.exists() System.out.println("文件名是：" + f.getAbsolutePath();System.out.println("文件大小是：" + f.length(); else f.getParentFile().mkdirs();try f.createNewFile(); catch (IOException e) e.printStackTrace();public class TestString1 public sta

41、tic void main(String args) String s1 = "hello"String s2 = "world"String s3 = "hello"System.out.println(s1 = s3); /trues1 = new String("hello");s2 = new String("hello");System.out.println(s1 = s2);System.out.println(s1.equals(s2);28 求下列String s = &quo

42、t;du*JG"中大写字母和小写字母，和其他个字符各多少个？public class TestString2 public static void main(String args) String s = "du*JG"String lStr = "abcdefghijklmnopqrstuvwxyz"String uStr = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"int lCount = 0;int uCount = 0;int oCount = 0;for(int i=0; i<s.length

43、(); i+) char c = s.charAt(i);if(lStr.indexOf(c) != -1) lCount +; else if(uStr.indexOf(c) != -1) uCount +; else oCount +;System.out.print(lCount + " " + uCount + " " + oCount);29 求java这个字符串在下列字符串中出现的次数String s = "5454javaadsfjavaadfasfjavasdfajavaaadfjavaADFAjava545"publ

44、ic class TestString3 public static void main(String args) String s = "5454javaadsfjavaadfasfjavasdfajavaaadfjavaADFAjava545"int count = 0;while(s.indexOf("java") != -1) s = s.substring(s.indexOf("java") + "java".length();count +;System.out.println(count);30 将文

45、件复制到新的位置import java.io.*;public class FileCopy public static void main(String args) int b = 0; FileReader in = null; FileWriter out = null; try in = new FileReader("d:/share/java/HelloWorld.java"); out = new FileWriter("d:/share/java/io/HW.java"); while(b=in.read()!=-1) out.write

46、(b); out.close(); in.close(); catch (FileNotFoundException e2) System.out.println("找不到指定文件"); System.exit(-1); catch (IOException e1) System.out.println("文件复制错误"); System.exit(-1); System.out.println("文件已复制"); 31 缓冲区字节流举例import java.io.*;public class TestBufferStream1 p

47、ublic static void main(String args) try FileInputStream fis = new FileInputStream("E:/EclipseCode_MyEclipse/Chapter8/src/TestBufferStream1.java"); BufferedInputStream bis = new BufferedInputStream(fis); int c = 0; System.out.println(bis.read(); System.out.println(bis.read(); bis.mark(100); for(int i=0;i<=10 && (c=bis.read()!=-1;i+) System.out.