Java——第四章（数组和字符串）项目案例

1。二维数组的应用，键盘输入9 个double类型数据，将数据转为int型。

import java.util.Scanner;public class Demo07 {public static void main(String[] args) {Scanner sc = new Scanner(System.in);double a[][]= new double [3][3];System.out.println("输入9个数");for(int i =1;i<=3;i++){for(int j =1;j<=3;j++){a[i-1][j-1] = sc.nextDouble();}}System.out.println("这些数为：");for(double[] b:a){for(double c:b)System.out.print(c+" ");}System.out.println();int b[][]= new int[3][3];for(int i = 1;i<=3;i++){for(int j =1;j<=3;j++){b[i-1][j-1] = (int) a[i-1][j-1];}}System.out.println("转为int数组数为：");for(int[] c:b){for(int d:c)System.out.print(d+" ");}}}

以上最后输出用的是foreach循环打印，输出语句同样可以用两个for循环遍历二维数组。

2.斐波那契数列

1 1 2 3 5 8.。。。。30数字是多少？

public class Demo01 {public static void main(String[] args) {/* * 斐波那契数列 1+1+2+3+5+。。。。。 */int a[] = new int[30];a[0] = a[1] = 1;for (int j = 1; j <= a.length - 2; j++) {a[j + 1] = a[j] + a[j - 1];}System.out.println(a[29]);for (int b : a) {System.out.print(b + " ");}}}

3.杨辉三角

1
1 1
1 2 1
1 3 3 1
1 4 6 4 1

public class Demo08 {// 五子棋。。1024的逻辑public static void main(String[] args) {// TODO Auto-generated method stubint a[][] = new int[10][10];for (int i = 0; i < 10; i++) {for (int j = 0; j < 10; j++) {if (j == 0 || i == j) {a[i][j] = 1;} else if ((j < i && j >= 1) && (i >= 2 && i < 10)) {a[i][j] = a[i - 1][j - 1] + a[i - 1][j];} else {a[i][j] = 0;}}}for (int i = 0; i < 10; i++) {for (int j = 0; j <= i; j++)System.out.print(a[i][j] + "\t");System.out.println();}}}

3.实现这样一个数组，一个顺时针递增。

1  2 3  4 5
16 17 18 19 6
15 24 25 20 7
14 23 22 21 8
13 12 11 10 9

public class Dem09 {public static void main(String[] args) {// TODO Auto-generated method stub/* * 1 2 3 4 5 16 17 18 19 6 15 24 25 20 7 14 23 22 21 8 13 12 11 10 9 *  */int a[][] = new int[5][5];for (int i = 0; i < 5; i++) {for (int j = 0; j < 5; j++) {if (i == 0) {a[i][j] = j + 1;}if (i == 1 && j <= 3) {a[i][j] = j + 16;}if ((i == 2) && (j == 1 || j == 2)) {a[i][j] = j + 23;}}}for (int i = 0; i < 5; i++) {for (int j = 0; j < 5; j++) {if (j == 4) {a[i][j] = 5 + i;}if ((j == 3) && (i >= 1 && i <= 3)) {a[i][j] = 18 + i;}}}for (int i = 0; i < 5; i++) {for (int j = 0; j < 5; j++) {if (i == 4)a[i][j] = 13 - j;if ((i == 3) && (j == 1 || j == 2 || j == 3)) {a[i][j] = 24 - j;}}}for (int i = 0; i < 5; i++) {for (int j = 0; j < 5; j++) {if ((j == 0) && (i >= 1))a[i][j] = 17 - i;if ((j == 2) & (i == 2))a[i][j] = 27 - i;if ((j == 2) & (i == 3))a[i][j] = 25 - i;}}for (int i = 0; i < 5; i++) {for (int j = 0; j < 5; j++) {System.out.print(a[i][j] + "\t");}System.out.println();}}}

4.判断输入的是否是邮箱地址

import java.util.Scanner;public class Demo13 {/* * 判断输入的是否是邮箱地址 */public static void main(String[] args) {// TODO Auto-generated method stubwhile (true) {Scanner sc = new Scanner(System.in);System.out.println("输入邮箱地址：");String s = sc.next();// boolean bo =s.indexOf("@")!=-1;if ((s.contains("@")) && s.endsWith(".com") && (s.indexOf(".") - s.indexOf("@") > 1)&& s.indexOf("@") > 0) {System.out.println(s + "为邮箱地址");} elseSystem.out.println("邮箱地址输入有误！");}}}

5.首先让计算机随机产生出10个两位正整数，然后按照从小到大的次序显示出来。

import java.util.Arrays;import java.util.Random;import java.util.Scanner;public class Demo14 {public static void main(String[] args) {// TODO Auto-generated method stub//1.首先让计算机随机产生出10个两位正整数，然后按照从小到大的次序显示出来。int a[] = new int[10];Scanner sc = new Scanner(System.in);Random r = new Random();System.out.println("输入十个数：");for (int i = 0; i < a.length; i++) {a[i]= r.nextInt(90)+10;}Arrays.sort(a);for (int i = 0; i < a.length; i++) {System.out.print(a[i]+" ");}for (int i = 0; i < a.length; i++) {for(int j = 0;j< a.length-i-1;j++){if(a[j]>a[j+1]){int temp = a[j];a[j] = a[j+1];a[j+1] = temp;}}}System.out.println("排序后：");for (int i = 0; i < a.length; i++) {System.out.print(a[i]+" ");} }}

6.从键盘上输入4行4列的一个实数矩阵到一个二维数组中，然后求出主对角线上元素之乘积以及副对角线上元素之乘积。

import java.util.Arrays;import java.util.Random;import java.util.Scanner;public class Demo14 {public static void main(String[] args) {System.out.println("输入4*4的数组");int b [][] = new int [4][4];for (int i = 0; i < 4; i++) {for (int j = 0; j < 4; j++) {b[i][j]= sc.nextInt();}}int ji =1;for (int i = 0; i < b.length; i++) {for (int j = 0; j < b.length; j++) {if(i == j){ji = ji*b[i][j];}}}System.out.println("主对角线成绩为："+ji);int ji2 =1;for (int i = 0; i < 4; i++) {for (int j = 0; j <4; j++) {if(i+j==3)ji2 = ji2*b[i][j];}}System.out.println("副对角线成绩为："+ji2);}}

7.输入字符串，大写到小写的转换，输出前后字符调换的结果。

import java.util.Arrays;import java.util.Random;import java.util.Scanner;public class Demo14 {public static void main(String[] args) {String s = sc.next();String s1 = s.toLowerCase();//System.out.println("大写变小写："+s1);String s2 = s1.toUpperCase();//System.out.println("小写变大写："+s2);char[] c = s.toCharArray();for (int i = 0; i < c.length/2; i++) {int oldindex = i;int newindex = c.length-1-i;char temp = c[oldindex];c[oldindex] = c[newindex];c[newindex] = temp;}System.out.println("交换后的字符串");String str =new String(c);System.out.println(c);}}