java学习笔记上

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//switch语句
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public class Swich {
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public static void main(String[] args) {
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Scanner sc = new Scanner(System.in);
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System.out.print("请输入您的选择:");
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int choose = sc.nextInt();
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switch (choose) {
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case 1:
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System.out.println("机票查询");
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break;
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case 2:
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System.out.println("机票预订");
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break;
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case 3:
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System.out.println("机票改签");
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break;
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case 4:
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System.out.println("退出服务");
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break;
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default:
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System.out.println("输入有误");
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break;

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//未知数求和
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import java.util.Scanner;
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public class
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arrtest6 {
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public static void main(String[] args){/main方法名
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int[]arr=new int[5];//不知道放什么
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Scanner sc=new Scanner(System.in);
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for (int i = 0; i < arr.length; i++) {
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System.out.println("请输入数组中的数字");
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int num=sc.nextInt();//每次输入
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arr[i]=num;//把输入的数字放入数组中
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}
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intsum=0;//遍历求和
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for (int i = 0; i < arr.length; i++) {sum=arr[i+sum;
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}
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System.out.println(sum);

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public static void main(String[] args) {
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//int[][] arr = new int[3][4];//创建二维数组不知道内容
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int[][] arr = {{1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10,11,12}};//知道内容
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//获取6
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System.out.println(arr[1][1]);
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//遍历二维数组
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for (int i = 0; i < arr.length; i++) {
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for (intj=0;j<arr[i].length;j++){
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System.out.print(arr[i][j]+" ");
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//迭代器循环
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    for (int[] ints:arr){
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for (int anInt : ints){
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System.out.println(anInt);
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System.out.println();//换行嵌套在循环以内
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}
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}
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//不知道二维数组的内容
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//int [][]arr=new int[3][4];
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//3为二维数组的行数,4为二维数组的列数

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public class arr5 {
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public static void main(String[] args) {
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//创建一个6的int数组 元素在1-30 是随机赋值 而且元素值各不相同
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int[] arr = new int[6];
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for (int i = 0;i<arr.length;i++){
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boolean count = true;
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int value = (int)(Math.random()*29 + 1);
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for (int j = 0;j<=i;j++) {
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if(value==arr[j])//如果有和前面相同的就false 不打和
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count = false;
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i--;//这次没有加入数据 重新来
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break;
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if(count){
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arr[i] = value;
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for (int name : arr){
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System.out.println(name);
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}
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}

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public class arr6{
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public static void main(String[] args) {
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String[] arr = new String[]{"JJ", "DD", "CC", "XX","YY"};
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String[] arr1 = new String[arr.length];
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//数组的复制(和arr1=arr不同)
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System.arraycopy(arr, srcPos: 0, arr1, destPos: 0, arr.length);
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for (String arr01 : arr1){
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System.out.print(arr01 + " ");
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System.out.println();
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System.out.print("方法一:");
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//数组的反转
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//方法一
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for (intj=0;j<arr.length/2;ji++){
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String temp = arr[j];
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arr[j] = arr[arr.length - j - 1];
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arr[arr.length - j - 1] = temp;
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for (String arr02 : arr){
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System.out.print(arr02 + " ");
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}
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}
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//方法二再把arr返一下
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System.out.println();
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System.out.print("方法二:");
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for (inti= 0,j = arr.length - 1; i <j; i++,j--){
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String temp2 = arr[i];
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arr[i] = arr[j];
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arr[j] = temp2;
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for (String arr02 : arr){
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System.out.print(arr02 + " ");

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import java.util.Scanner;
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public class arrtest01{
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public static void main(String[] args) {
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Scanner input = new Scanner(System.in);
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String[] arr = new String[]{"JJ", "DD", "CC", "XX", "XX", "٧٧"};
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//线性查找
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System.out.print("请输入你要查找的字符:");
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String test = input.nextline();
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boolean count = true;
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for (int a = 0; a < arr.length; a++) {
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if(test.equals(arr[a])) {
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System.out.print("找到了指定元素的位置");
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System.out.println(a);
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count = false;
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break;
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(count)
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System.out.println("很遗憾,没找到");
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}

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public static void main(String[] args) {
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int[] arr1 = new int[]{-89, -6, 1, 6, 7, 23, 44,77,80,82}
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Scanner input = new Scanner(System.in);
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System.out.print("请输入你要查找的数字:");
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int test1 = input.nextInt();
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int start=0;
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int end = arr1.length - 1;
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while (start<= end){
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int middle = (start + end) / 2;
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if(test1== arr1[middle]) {
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System.out.println("找到了指定元素,位置:"+"["+middle + "]");
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break;
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} else if (arr1[middle] > test1) {
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end = middle - 1;
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}else{
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start = middle + 1;
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}
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if(start>end){
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System.out.println("未找到指定元素");
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}
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input.close();

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public class ArrayTest03 {
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public static void main(String[] args) {
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//冒泡排序
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int [] arr = new int[]{-5٫-9,5,1,9,7,6,5,3,4};
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for (int i = 0;i<arr.length-1;i++){
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for (int j = 0;j < arr.length - 1 -i;j++){
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if (arr[j] > arr[j+1]){
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int temp = arr[j];
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arr[j] = arr[j+1];
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arr[j+1] = temp;
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}
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for (int num : arr){
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System.out.print(num+" ");
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}
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}

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import java.util.Random;
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import java.util.Scanner;
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public class arrtest9 {
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public static void main(String[] args) {
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1储存所有的大、小写字母
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char[] letts = new char[52];
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for (int i = 0;i<letts.length;i++){
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if(i<=25){
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//添加a~z
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letts[i] = (char)(97+i);
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}else {
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//添加A~Z
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letts[i] = (char)(65+i-26);
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}
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}
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//A转换为ASCII的值
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2、随机抽取数组中的索引
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Random r = new Random();
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String result = "";
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for (int i = 0; i < 4; i++) { //4.fori
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int randomData = r.nextInt(letts.length);
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result +=
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letts[randomData];
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3、随机抽取一个0-9的数字
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int num = r.nextint( bound: 10);
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result += num;
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System.out.println(result);
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}

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public class MethodTest1{
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public static void main(String[] args) { printlnfo();//调用函数 //主入口
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//方法使独立功能实现
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11定义格式
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//public static void
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//调用格式:方法名()
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方法名()
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//注意1.方法之间不能嵌套
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//2、方法需要被调用例如python中的def
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public static void printlnfo(){1个用法
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System.out.println("姓名小丹丹");
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System.out.println("年龄:18");
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System.out.println("性别:女");
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所有的方法都需要写在public class类名{}里面
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}

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class Person{
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5个用法
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//属性javabean
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intage=18;4个用法
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Stringnames;7个用法
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booleanisMale;1个用法
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//方法
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public void eat(String name){
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System.out.println(name+"要吃饭");
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public void play(String name){1个用法
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System.out.println(name+"喜欢玩游戏");
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}
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public void ages(String name,int age){1个用法
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System.out.println(name+"今年" + age+"岁");
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}
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public void talk(String language){1个用法
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System.out.println("全世界都在说"+language);
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public class classTest {
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public static void main(String[] args) {
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//创建Person类的对象
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Person p1 = new Person();
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√调用对象的结构:属性、方法
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调用属性:对象.属性
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p1.names="小明";
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p1.isMale = true;
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System.out.println(p1.names);
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p1.eat(p1.names);
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p1.play(p1.names);
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p1.ages(p1.names,p1.age);
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p1.talk(language:"中国话");
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System.out.println("p2
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Person p2 = new Person();
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System.out.println(p2.names);
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System.out.println(p2.age);
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System.out.println();
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*************************************
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System.out.println("p3 ***************
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*****************").
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Person p3 = p1;
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System.out.println(p3.names);
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//将p1 变量保存的对象地址赋给了p3导致 p1和p3指向同个堆
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p3.age = 21;
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System.out.println(p1.age);
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//自己的理解就是p1和p3是同一个p3是p1的别名

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属性(成员变量)vs局部变量
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public class oop1 {
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public static void main(String[] args) {
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User p1 = new User();
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System.out.println(p1.name);
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System.out.println(p1.age);
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System.out.println(p1.isMale);
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p1.talk(language:"中文");
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p1.eat();
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class User{2个用法
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//属性(成员变量)
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Stringname;1个用法
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public int age;
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booleanisMale;1个用法
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public void talk(String language){//Language形参 也是局部变量1个用法
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System.out.println("我们使用"+ language+"说话")
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public void eat(){String food="烙饼";// 局部变量
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System.out.println("北方人喜欢吃"+ food);

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public static void main(String[] args) {
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//计算1-100的自然数的和
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//方式一
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int sum = 0;
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for(int i =1;i<=100;i++){
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sum += i;
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}
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System.out.println(sum);
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//方式
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digui test = new digui(
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System.out.println(test.getSum(
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//例二
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num:100));
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System.out.println(test.f( num: 10));
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//斐波那契
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System.out.println(test.fibonacci( num: 10));
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 public int getSum(int num){2个用法
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if(num== 1){
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return 1;
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return num + getsum(num: num-1);
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//例题有一个数列f(0)=1,f(1)=4,f(n+2)=2*f(n+1)+f(n)
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//求f(10)
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public int f(int num){ 3个用法
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if(num=== 0){
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return 1;
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else if (num == 1){
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return 4;
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return f( num: num-2) + (2*f( num-1));
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}

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public class AnimalTest {
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public static void main(String[] args)
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Animal animal = new Animal
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animal.name="大黄";
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animal.age = 5;
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animal.setLegs(4);
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System.out.println(animal.getlegs
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animal.show();
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animal.eat
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class Animal{2个用法
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Stringname;2个用法
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intage;2个用法
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private int legs;
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//属性的设置
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//private 4个用法
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// 快捷键alt+insert
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//ptg一秒生成javaBean类
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public void setlegs(int 1){1个用法
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if(1>0 0 & 1 % 2 == 0){
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legs = l;
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else {
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legs = 0;
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//属性的获取
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public int getlegs(){ 1个用法
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return legs;
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public void eat(){
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System.out.println("吃东西");

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package oop;
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public class constructor2 {
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public static void main(String[] args) {
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User user = new User();
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System.out.println(user.age);
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User user1 = new User( a: 2);
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user1.setAge(4);
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System.out.println(user1.age);
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}
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}
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class User{
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String name;|
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1个用法
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int age=1;
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public User(){
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1个用法
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//空参构造
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}
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public User(inta){ 1个用法
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age = a;
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//赋值 构造器中括号中参数
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}
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public void setAge(int a){
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age = a;

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class Chinese{
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String name;
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int age;
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static String nation;
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public void eat(){
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System.out.println("我要吃饭");
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public static void show(){
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System.out.println("我是一个中国人!");
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//不能调用非静态结构 eat() name:= "Tom"方法和属性
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System.out.println(Chinese.nation);
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walk();//静态方法
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System.out.println("nation : "+ nation);
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public static void walk(){
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System.out.println("走路");
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public void info(){
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System.out.println("name = " + name + " age = " + age)
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public class StaticTest {
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public static void main(String[] args) {
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Chinese.nation="中国人";
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Chinese chinese1 = new Chinese();
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chinese1.name="汪大东";
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chinese1.age = 28;
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Chinese chinese2 = new Chinese
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chinese2.name="金宝三";
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chinese2.age = 34;
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Chinese chinese3 = new Chinese
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chinese3.name="林丹";
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chinese3.age = 32;
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Chinese.show() ;