JAVA学习第四天
来源：互联网 发布：知呱呱 编辑：程序博客网 时间：2024/05/08 21:43
目录
1.数组兔子数
2.数组成绩平均数
3.冒泡法排序
4.九宫格
5.自动排序和复制指定数组
6.求数组中的最大值
7.concat contains copyValueOf的使用
8.字符串是否相等
9.是否为合法的邮箱名
10.10个100以内随机的两位数从小到大排序
11.字符转数组
12.大写变小写小写变大写
13.X乘X矩阵的主对角线乘积和副对角线乘积
14.右边数三位加逗号
15.数组的写法
16.copyValueOf
数组兔子数
package Test;public class Demo兔子数 { /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub int[] array=new int[10];// int[] array={1,2,3,0,0,0,0,0,0,0};// int[] array=new int[]{1,2,3,0,0,0,0,0,0,0}; 三种写法 array[0]=1; array[1]=2; array[2]=3; for(int i=3;i<array.length;i++){ array[i]=array[i-3]+array[i-1]; } System.out.println(array[9]); }}数组成绩平均数
package Test;import java.util.Scanner;public class Dome数组成绩平均数{ /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub double[] score=new double[5]; for (int i = 0; i < score.length; i++) { Scanner scanner=new Scanner(System.in); score[i]=scanner.nextDouble(); } double s=0; for (int i = 0; i < score.length; i++) { s+=score[i]; } System.out.println("平均数>"+s/score.length); }}冒泡法排序
package Test;public class Demo冒泡排序 { /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub int[] score=new int[]{80,72,65,43}; int temp=0; for (int i = 0; i < score.length-1; i++) { for (int j = 0; j < score.length-i-1; j++) { if(score[j]>score[j+1]){ temp=score[j+1]; score[j+1]=score[j]; score[j]=temp; } } }for (int i = 0; i < score.length; i++) { System.out.println(score[i]);} }}九宫格
package Test;public class Demo九宫格 { /** * @param args */ public static void main(String[] args) { // TODO Auto-generated method stub int [][] array=new int[3][]; array[0]=new int[]{4,9,2}; array[1]=new int[]{3,5,7}; array[2]=new int[]{8,1,6}; for (int i = 0; i < array.length; i++) { int item[]=array[i]; for (int j = 0; j < item.length; j++) { System.out.print(item[j]+"\t"); } System.out.println(); } }}自动排序和复制指定数组
package com.zhonghang.svn;import java.util.Arrays;public class Test2 { public static void main(String[] args){ int[] array=new int[]{1,2,4,3,5,7,6,8,9}; Arrays.sort(array);//自动排序 int[] arra={2,3,6,5,4}; int score[]=new int[5]; //score=Arrays.copyOf(array, 3);//从0-2 包头不包尾 //score=Arrays.copyOfRange(array, 1, 4);//从1-3 不包含4 for (int i = 0; i < array.length; i++) { System.out.println(array[i]); } }}求数组中的最大值
package com.zhonghang.svn;import java.util.Arrays;public class Test2 { public static void main(String[] args){ int[] arr=new int[]{64,75,72,36,89}; int max=0; for (int i = 0; i < arr.length; i++) { if(arr[i]>max){ max=arr[i]; } }System.out.println(max); }}concat contains copyValueOf的使用
package com.zhonghang.svn;import java.util.Arrays;public class Test2 { public static void main(String[] args){ String s="nihao"; String s1="zaoshanghao"; char[] c={'a','b','v','f'}; //System.out.println(s.concat(s1));//concat 相当于+ //System.out.println(s.contains("ni"));//是否包含字符 ni为true; nh为false String s2=String.copyValueOf(c);//复制指定字符 String s3=String.copyValueOf(c, 0, 2);//复制一段字符 包头不包尾 System.out.println(s3); }}
字符串是否相等
package Test;public class Demo1 { /** * @param args */ public static void main(String[] args) { // TODO 自动生成的方法存根 String aa=new String("abcd"); String bb=aa; String cc=new String("abcd"); String dd="abcd"; String ff="abcd"; System.out.println(bb.equals(aa));//true System.out.println(cc.equals(aa));//true System.out.println(bb==aa);//true System.out.println(cc==aa);//地址不一样//false System.out.println(dd==aa);//aa为新建的 两者地址不一样//false System.out.println(ff==dd);//建立了一个abcd常量//true }}是否为合法的邮箱名
package com.zhonghang.svn;import java.util.Scanner;public class Test1 { public static void main(String[] args) { // TODO Auto-generated method stub while(true){ Scanner scanner = new Scanner(System.in); String email = scanner.nextLine(); boolean isEmail=false; if (email.contains("@")) { if (email.indexOf('@') == email.lastIndexOf('@')) { String emailStart = email.substring(0, email.indexOf('@')); boolean isLetterOrNum_Start = isLetterOrNum(emailStart); if (isLetterOrNum_Start) { if (email.endsWith(".com") || email.endsWith(".cn") || email.endsWith(".net")) { String emailMiddle=email.substring(email.indexOf('@')+1,email.lastIndexOf('.')); isEmail=isLetterOrNum(emailMiddle); } } } if(isEmail){ System.out.println("正确的Email"); }else{ System.out.println("错误的Email"); } } } } public static boolean isLetterOrNum(String s) { boolean isLetterOrNum_ = false; for (int i = 0; i < s.length(); i++) { char c = s.charAt(i); if (Character.isLetter(c) || Character.isDigit(c) || c == '_') { isLetterOrNum_ = true; break; } } return isLetterOrNum_; }}10个100以内随机的两位数从小到大排序
package Test;import java.util.Arrays;import java.util.Random;public class Demosuijishucongxiaodaodapialie { public static void main(String[] args) { // TODO Auto-generated method stub int[] arr = new int[10]; for (int i = 0; i < 10; i++) { Random r = new Random(); int a = r.nextInt(90) + 10;//变换 arr[i] = a; } // Arrays.sort(arr); for (int i = 0; i < arr.length; i++) { for (int j = 0; j < arr.length - i - 1; j++) { int temp = 0; if (arr[j] > arr[j + 1]) { temp = arr[j + 1]; arr[j + 1] = arr[j]; arr[j] = temp; } } } for (int i = 0; i < 10; i++) { System.out.print(arr[i] + " "); } System.out.print(Arrays.toString(arr));// 数组的两种输出方法 }}字符转数组
package Test;public class Demozifuzhuanshuzu { public static void main(String[] args) { // TODO Auto-generated method stub // TODO Auto-generated method stub String s = new String("abc,dc,fg"); String[] array = s.split(",");//字符串数组 for (int i = 0; i < array.length; i++) { System.out.println(array[i]); } System.out.println(s.substring(2, 6)); }}大写变小写小写变大写
package Test;public class Demodaxiebianxiaoxiexiaoxiebiandaxie { public static void main(String[] args) { // TODO Auto-generated method stub String s = "acdBDS"; String s2 = " "; for (int i = 0; i < s.length(); i++) { char c = s.charAt(i); if (Character.isLowerCase(c)) {//是否是小写 c = Character.toUpperCase(c);//变为大写 } else { c = Character.toLowerCase(c);//变为小写 } // if(c>='a'&&c<='z'){ // c=(char)(c-32); // }else if(c>='A'&&c<='Z'){ // c=(char)(c+32); // // } s2 = s2.concat(" " + c); } System.out.println(s2); }}X乘X矩阵的主对角线乘积和副对角线乘积
package com.zhonghang.svn;import java.util.Random;public class Test4 { public static void main(String[] args) { // TODO Auto-generated method stub int indexMax = 4; int[][] array = new int[indexMax][indexMax]; for (int i = 0; i < indexMax; i++) { for (int j = 0; j < indexMax; j++) { Random random = new Random(); array[i][j] = random.nextInt(9) + 1; } } for (int i = 0; i < indexMax; i++) { for (int j = 0; j < indexMax; j++) { System.out.print(array[i][j] + "\t"); } System.out.println(); } int s1 = 1; int s2 = 1; for (int i = 0; i < indexMax; i++) { s1 = s1 * (array[i][i]); s2 = s2 * (array[i][indexMax - 1 - i]); } System.out.println("主对角线乘积" + s1); System.out.println("副对角线乘积" + s2); }}右边数三位加逗号
package Test;public class Demoyoubiansanweijiadouhao { public static void main(String[] args) { // TODO Auto-generated method stub // TODO Auto-generated method stub StringBuffer sb = new StringBuffer("78778945641123214"); // for (int i = 3; i < sb.length(); i+=4) { // sb.insert(i,","); // // } // // System.out.println(sb);//左边数三个插入一个逗号 for (int i = (sb.length() - 3); i > 0; i -= 3) { sb.insert(i, ","); } System.out.println(sb);// 右边数三位一个逗号 }}完善的Email1
package Test;import java.util.Scanner;public class DemowanshandeEmail1 { public static void main(String[] args) { while (true) { Scanner scanner = new Scanner(System.in); String email = scanner.nextLine(); boolean isEmailContain = false; boolean emailStartisLetterOrNum_1 = false; boolean emailMiddleisLetterOrNum_1 = false; if (email.contains(".")) { if (email.indexOf('.') == email.lastIndexOf('.')) {// 如果一个点 if (email.contains("@")) { if (!(email.contains("@."))) { if (email.indexOf('@') == email.lastIndexOf('@')) { if (email.endsWith(".com") || email.endsWith(".cn") || email.endsWith(".net")) { isEmailContain = true; } } } } String emailStart = email.substring(0, email.indexOf('@')); char c1 = emailStart.charAt(0); if (Character.isLetter(c1)) { for (int i = 1; i < emailStart.length(); i++) { boolean emailStartisLetterOrNum_ = false; char c = emailStart.charAt(i); if (Character.isLetter(c) || Character.isDigit(c) || c == '_') { emailStartisLetterOrNum_ = true; emailStartisLetterOrNum_1 = emailStartisLetterOrNum_; } else { emailStartisLetterOrNum_ = false; emailStartisLetterOrNum_1 = emailStartisLetterOrNum_; break; } } String emailMiddle = email.substring(email.indexOf('@') + 1, email.lastIndexOf('.')); for (int j = 0; j < emailMiddle.length(); j++) { boolean emailMiddleisLetterOrNum_ = false; char c2 = emailMiddle.charAt(j); if (Character.isLetter(c2) || Character.isDigit(c2) || c2 == '_') { emailMiddleisLetterOrNum_ = true; emailMiddleisLetterOrNum_1 = emailMiddleisLetterOrNum_; } else { emailMiddleisLetterOrNum_ = false; emailMiddleisLetterOrNum_1 = emailMiddleisLetterOrNum_; break; } } } if (emailStartisLetterOrNum_1 && emailMiddleisLetterOrNum_1 && isEmailContain) { System.out.println("正确的Email"); } else { System.out.println("错误的Email"); } }else { // 如果一个点 if (email.contains("@")) { if (!(email.contains("@."))) { if (email.indexOf('@') == email.lastIndexOf('@')) { if (email.endsWith(".com") || email.endsWith(".cn") || email.endsWith(".net")) { isEmailContain = true; } } } } String emailStart = email.substring(0, email.indexOf('@')); char c1 = emailStart.charAt(0); if (Character.isLetter(c1)) { for (int i = 1; i < emailStart.length(); i++) { boolean emailStartisLetterOrNum_ = false; char c = emailStart.charAt(i); if (Character.isLetter(c) || Character.isDigit(c) || c == '_') { emailStartisLetterOrNum_ = true; emailStartisLetterOrNum_1 = emailStartisLetterOrNum_; } else { emailStartisLetterOrNum_ = false; emailStartisLetterOrNum_1 = emailStartisLetterOrNum_; break; } } String emailMiddle1 = email.substring(email.indexOf('@') + 1, email.indexOf('.')); for (int j = 0; j < emailMiddle1.length(); j++) { boolean emailMiddleisLetterOrNum_ = false; char c2 = emailMiddle1.charAt(j); if (Character.isLetter(c2) || Character.isDigit(c2)||c2=='_' ) { emailMiddleisLetterOrNum_ = true; emailMiddleisLetterOrNum_1 = emailMiddleisLetterOrNum_; } else { emailMiddleisLetterOrNum_ = false; emailMiddleisLetterOrNum_1 = emailMiddleisLetterOrNum_; break; } } String emailMiddle2 = email.substring(email.indexOf('.') + 1, email.lastIndexOf('.')); char c3=emailMiddle2.charAt(0); if(Character.isLetter(c3)){ for (int j = 1; j < emailMiddle2.length(); j++) { boolean emailMiddleisLetterOrNum_ = false; char c2 = emailMiddle2.charAt(j); if (Character.isLetter(c2) ) { emailMiddleisLetterOrNum_ = true; emailMiddleisLetterOrNum_1 = emailMiddleisLetterOrNum_; } else { emailMiddleisLetterOrNum_ = false; emailMiddleisLetterOrNum_1 = emailMiddleisLetterOrNum_; break; } } }else if ( Character.isDigit(c3)) { for (int j = 1; j < emailMiddle2.length(); j++) { boolean emailMiddleisLetterOrNum_ = false; char c2 = emailMiddle2.charAt(j); if (Character.isDigit(c2) ) { emailMiddleisLetterOrNum_ = true; emailMiddleisLetterOrNum_1 = emailMiddleisLetterOrNum_; } else { emailMiddleisLetterOrNum_ = false; emailMiddleisLetterOrNum_1 = emailMiddleisLetterOrNum_; break; } } } if (emailStartisLetterOrNum_1 && emailMiddleisLetterOrNum_1 && isEmailContain) { System.out.println("正确的Email"); } else { System.out.println("错误的Email"); } } } } }}}完善的Email2
package Test;import java.util.Scanner;public class DemowanshandeEmail2 { public static void main(String[] args) { // TODO Auto-generated method stub while (true) { Scanner scanner = new Scanner(System.in); String email = scanner.nextLine(); boolean isEmailContain = false; boolean emailStartisLetterOrNum_1 = false; boolean emailMiddleisLetterOrNum_1 = false; if (email.contains(".")) { if (email.contains("@")) { if (!(email.contains("@."))) { if (email.indexOf('@') == email.lastIndexOf('@')) { if (email.endsWith(".com") || email.endsWith(".cn") || email.endsWith(".net")) { isEmailContain = true; } } } } String emailStart = email.substring(0, email.indexOf('@')); char c1 = emailStart.charAt(0); if (Character.isLetter(c1)) { for (int i = 1; i < emailStart.length(); i++) { boolean emailStartisLetterOrNum_ = false; char c = emailStart.charAt(i); if (Character.isLetter(c) || Character.isDigit(c) || c == '_') { emailStartisLetterOrNum_ = true; emailStartisLetterOrNum_1 = emailStartisLetterOrNum_; } else { emailStartisLetterOrNum_ = false; emailStartisLetterOrNum_1 = emailStartisLetterOrNum_; break; } } if (email.indexOf('.') == email.lastIndexOf('.')) { // 如果一个点 String emailMiddle = email.substring(email.indexOf('@') + 1, email.lastIndexOf('.')); for (int j = 0; j < emailMiddle.length(); j++) { boolean emailMiddleisLetterOrNum_ = false; char c2 = emailMiddle.charAt(j); if (Character.isLetter(c2) || Character.isDigit(c2) || c2 == '_') { emailMiddleisLetterOrNum_ = true; emailMiddleisLetterOrNum_1 = emailMiddleisLetterOrNum_; } else { emailMiddleisLetterOrNum_ = false; emailMiddleisLetterOrNum_1 = emailMiddleisLetterOrNum_; break; } } if (emailStartisLetterOrNum_1 && emailMiddleisLetterOrNum_1 && isEmailContain) { System.out.println("正确的Email"); } else { System.out.println("错误的Email"); } } else { // 不是一个'.'的情况下 String emailMiddle1 = email.substring(email.indexOf('@') + 1, email.indexOf('.')); for (int j = 0; j < emailMiddle1.length(); j++) { boolean emailMiddleisLetterOrNum_ = false; char c2 = emailMiddle1.charAt(j); if (Character.isLetter(c2) || Character.isDigit(c2) || c2 == '_') { emailMiddleisLetterOrNum_ = true; emailMiddleisLetterOrNum_1 = emailMiddleisLetterOrNum_; } else { emailMiddleisLetterOrNum_ = false; emailMiddleisLetterOrNum_1 = emailMiddleisLetterOrNum_; break; } } String emailMiddle2 = email.substring(email.indexOf('.') + 1, email.lastIndexOf('.')); char c3 = emailMiddle2.charAt(0); if (Character.isLetter(c3)) { for (int j = 1; j < emailMiddle2.length(); j++) { boolean emailMiddleisLetterOrNum_ = false; char c2 = emailMiddle2.charAt(j); if (Character.isLetter(c2)) { emailMiddleisLetterOrNum_ = true; emailMiddleisLetterOrNum_1 = emailMiddleisLetterOrNum_; } else { emailMiddleisLetterOrNum_ = false; emailMiddleisLetterOrNum_1 = emailMiddleisLetterOrNum_; break; } } } else if (Character.isDigit(c3)) { for (int j = 1; j < emailMiddle2.length(); j++) { boolean emailMiddleisLetterOrNum_ = false; char c2 = emailMiddle2.charAt(j); if (Character.isDigit(c2)) { emailMiddleisLetterOrNum_ = true; emailMiddleisLetterOrNum_1 = emailMiddleisLetterOrNum_; } else { emailMiddleisLetterOrNum_ = false; emailMiddleisLetterOrNum_1 = emailMiddleisLetterOrNum_; break; } } } if (emailStartisLetterOrNum_1 && emailMiddleisLetterOrNum_1 && isEmailContain) { System.out.println("正确的Email"); } else { System.out.println("错误的Email"); } } } } } }}数组的写法
copy
字符串的声明与赋值
- String s=new String(“abc”);
在栈内存中开辟地址指向堆内存，在堆内存存放“abc”。 - String s =”abc”;
先在常量池中找“abc”，若没有则独立开辟内存空间存放“abc”。 - s.split(“char”):将字符串按 “char”分割为子字符串，结果作为字符串数组返回
- indexOf(“”或者”)该字符在字符串中第一次出现的索引值,若没有出现则返回-1.
indexOf(”,fromIndex)如果索引值>=fromIndex,则返回索引值;如果
str.trim().length()的使用
package com.donghe.svn;import java.util.Scanner;public class Test { public static void main(String[] args) { String str=" java hello ! "; System.out.println("字符串原来的长度:"+str.length());//结果为15 System.out.println("字符串去掉空格之后的长度"+str.trim().length());//去掉的是字符串str前导和尾部的空格后 结果为12 }}copyValueOf的使用
package com.donghe.svn0;import java.util.Arrays;public class Test { public static void main(String[] args) { char[] c=new char[]{'a','b','c','d'};//字符数组 for (int i = 0; i < c.length; i++) { System.out.print(c[i]); }System.out.println(Arrays.toString(c));System.out.println(String.valueOf(c));//将字符数组变成字符串System.out.println(String.copyValueOf(c));//返回c中所有元素构成的字符串 ，结果就是产生一个"abcd"字符串 System.out.println(String.copyValueOf(c,2,2));//返回由c中从下标2的元素（就是'c'）开始，长度为2的元素构成的字符串，结果就是产生一个"cd"字符串。 }}copyValueOf 和ValueOf
package com.donghe.svn0;import java.util.Arrays;public class Test { public static void main(String[] args) { char[] c=new char[]{'a','b','c','d'};//字符数组 for (int i = 0; i < c.length; i++) { System.out.print(c[i]); }System.out.println(Arrays.toString(c));System.out.println(String.valueOf(c));//将字符数组变成字符串System.out.println(String.copyValueOf(c));//返回c字符数组中所有元素构成的字符串 ，结果就是产生一个"abcd"字符串 已经与valueOf基本上没有区别了 System.out.println(String.copyValueOf(c,2,2));//返回由c中从下标2的元素（就是'c'）开始，长度为2的元素构成的字符串，结果就是产生一个"cd"字符串。 }}str.lastIndexOf(“”)
package com.donghe.svn;import java.util.Scanner;public class Test { public static void main(String[] args) { String str="we are students"; System.out.println(str.lastIndexOf(""));//空字符串注意没有空格 从0开始 其返回结果与调用该字符串length()的返回结果相同 System.out.println(str.length()); }} 0 0
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