數組
- 先聲明
- 申請空間
- 賦值
一維數組
方式1：int arr[ ] = { 1,2,3,4,5,6};
方式2：int arr1[ ] = new int[ 6 ];
arr[ 0 ] = 1;
arr[ 1 ] = 2;
arr[ 2 ] = 3;
arr[ 3 ] = 4;
arr[ 4 ] = 5;
arr[ 5 ] = 6;
方式3：
int arr2[ ] = new int [ ]{ 1,2,3,4,5,6};
二維數組
//1聲明方式 中括號中不能指定個數
int[][] arr1;
int[] arr2[];
int arr3[][];
//2給數組賦值（初始化）
arr1 = new int[3][4];
arr2 = new int[4][];//第二個括號可以不指定個數
arr3 = new int[][4];//錯誤。
//給二維數組arr3申請空間（特殊情況）
arr3 = new int[3][];
arr3[0] = new int[5];
arr3[1] = new int[6];
arr3[2] = new int[4];
//賦值
arr1[0][0] = 34;
arr3[0][0] = 3;
arr3[0][1] = 4;
arr3[0][2] = 5;
//二維數組的遍歷
//方法1
for (int i = 0; i < arr3.length; i++) {
for (int j = 0; j < arr3[i].length; j++) {
System.out.print(arr3[i][j]+" ");
}
System.out.println();
}
System.out.println("************");
//方法2:
//遍歷二維數組中的每一個一維數組
for (int[] arr : arr3) {
//遍歷一維數組中的每一個元素
for (int cell : arr) {
System.out.print(cell+" ");
}
System.out.println();
}
運行結果:
數組排序方法
//1Eclipse裏自帶排序的方法
Arrays.sort(arr[i]);
Arrays.parallelSort(arr[i]);
int[] arr2 = {4,5,6,1,6,7,8,13,15};
//2將arr2的前n個元素賦給arr3
int[] arr3 = Arrays.copyOf(arr2, n);
//3選擇性的賦值（將arr2的第m個元素到n-1個元素賦給arr3）
//不包含to(第n個元素)位置
arr3 = Arrays.copyOfRange(arr2, m, n);
System.out.println(Arrays.toString(arr3));
//4填充(如果arr3本來就有元素，填充後新數組元素代替了前面的元素)
int[] arr3 = {4,5,6,1,6,7,8,13,15};
Arrays.fill(arr3, 888);
//5將arr3的第m個元素到n-1個元素之間的元素被新賦值爲999；
Arrays.fill(arr3, m, n, 999);
//6判斷兩個數組的所有元素是否相等。返回值爲True和False;
Arrays.equals(arr5, arr6)
//7判斷字符串數組arr[i]的元素是否等於abc
"abc".equals(arr[i])
字符串拼接操作
//將字符串中的每個字符取出放入到一個字符數組中
String str=“abcdefghjkl”;
//toCharArray()方法將此字符串轉換爲一個新的字符數組。
char[] cs = str.toCharArray();
//定義一個字符串拼接的操作的類
StringBuffer sBuffer = new StringBuffer();
for(char c :cs) {//c爲每次循環的變量，cs爲每個字符
char c2 = (char)(c^MY);
sBuffer.append(c2);
}
number = input.nextInt();
int newnumber = number%7;
6. 2
22
222
2222打印這種數字：代碼如下； p=p*10+2;
7. 輸入一個字符串原碼轉密文，又轉原文的題型。
package question1;
import java.nio.charset.Charset;
public class Mingmiwenzhuanhuan_question1 {
//key0是一種祕鑰
private static final String key0 = "FECOI()*&<MNCXZPKL";
private static final Charset charset = Charset.forName("UTF-8");
//getBytes()方法使用指定的字符集將此 String 編碼爲 byte 序列，並將結果存儲到一個新的 byte 數組中。
private static byte[] keyBytes = key0.getBytes(charset);
public static String encrypt(String enc) {
byte[] b = enc.getBytes(charset);
for (int i = 0, size = b.length; i < size; i++) {
for (byte keyBytes0 : keyBytes) {
b[i] = (byte) (b[i] ^ keyBytes0);
}
}
return new String(b);
}
public static String decode(String dec) {
byte[] e = dec.getBytes(charset);
byte[] dee = e;
for (int i = 0, size = e.length; i < size; i++) {
for (byte keyBytes0 : keyBytes) {
e[i] = (byte) (dee[i] ^ keyBytes0);
}
}
return new String(e);
}
public static void main(String[] args) {
String s = "you are right";
String enc = encrypt(s);
String dec = decode(enc);
System.out.println("加密後：" + enc);
System.out.println("解密後：" + dec);
}
}
8.一個年份有多少天
package lianxi1;
import java.util.Scanner;
public class Calc {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
boolean ist = true;
while (ist) {
System.out.println("請輸入一個年份");
int year = input.nextInt();
System.out.println("請輸入一年中的十二個月份中的任意一個月份！");
int month = input.nextInt();
while (month <= 0 || month > 12) {
System.out.println("你輸入的月份有誤，請重新輸入！");
month = input.nextInt();
}
int day=0 ;
boolean isTrue = true;
while (isTrue) {
System.out.println("請輸入一個日子");
day = input.nextInt();
if (month == 2 && month % 4 == 0 && month % 100 != 0) {
if (day <= 0 || day > 29) {
System.out.println("錯誤1:你輸入月份對應的天數有誤，請重新輸入！");
day = input.nextInt();
}else {
break;
}
}
if (month == 2 && month % 4 != 0 && month % 100 == 0) {
if (day <= 0 || day > 28) {
System.out.println("錯誤2:你輸入月份對應的天數有誤，請重新輸入！");
day = input.nextInt();
}else {
break;
}
}
if (month == 1 || month == 3 || month == 5 || month == 3 || month == 7 || month == 8 || month == 10
|| month == 12) {
if (day < 0 || day > 31) {
System.out.println("錯誤3:你輸入月份對應的天數有誤，請重新輸入！");
day = input.nextInt();
}else {
break;
}
}
if (month == 4 || month == 6 || month == 9 || month == 11) {
if (day <= 0 || day > 30) {
System.out.println("錯誤4:你輸入月份對應的天數有誤，請重新輸入！");
day = input.nextInt();
}else {
break;
}
}
isTrue = false;
}
int sumday = 0;
switch (month - 1) {
// 1 3 5 7 8 10 12 爲大月
// 4 6 9 11 爲小月
case 12:
sumday += day;
case 11:
sumday += 30;
case 10:
sumday += 31;
case 9:
sumday += 30;
case 8:
sumday += 31;
case 7:
sumday += 31;
case 6:
sumday += 30;
case 5:
sumday += 31;
case 4:
sumday += 30;
case 3:
sumday += 31;
case 2:
sumday += 28;
case 1:
sumday += 31;
}
if (month % 4 == 0 && month % 100 != 0) {
System.out.println(month + "月"+day+"日"+ "是一年的第" + (sumday + day) + "天");
}else if(month<2) {
System.out.println(month + "月"+day+"日"+ "是一年的第" + (sumday + day) + "天");
}
else {
System.out.println(month + "月"+day+"日"+ "是一年的第" + (sumday + day + 1) + "天");
}
}
}
}
9.1 9*9乘法表
package progect1_2;
public class Multiply1 {
public static void main(String[] args) {
for(int i=1;i<=9;i++) {
for(int j = 1;j<=i;j++) {
System.out.print(i+"*"+j+"= "+(i*j)+"\t\t");
}
System.out.println();
}
}
}
9.2 9*9乘法表
package progect1_2;
public class Multiply2 {
public static void main(String args[]) {
for (int i = 1, j = 1; i <= 9; j++) {
System.out.print( i + "*" + j + "=" + i * j+"\t");
if (i == j) {
//改變j的循環條件
j = 0;
i++;
System.out.println();
}
}
}
}
打印楊輝三角
package progect1_1;
public class Yanghui {
public static void main(String[] args) {
int arr[][] = new int[7][];
for (int i = 0; i < arr.length; i++) {//控制行數
arr[i] = new int [i+1];
for (int j = 0; j < arr[i].length; j++) {//控制列數
if (j == 0 || j == i ) {
arr[i][j] = 1;
}else {
arr[i][j] = arr[i-1][j]+arr[i-1][j-1];
}
System.out.print(arr[i][j]+" ");
}
System.out.println();
}
}
}
