学习自华为开发者学院JAVA系列课程
数据类型
数据类型转换（自动转换+强制转换）
public class AppleSal {
public static void main(String[] args){
int before = 20;
//Java 默认浮点数类型是double
//float rise = 9.8f;
double rise = 9.8;
double result = before + rise;
System.out.println("今年苹果笔记本销售额为: "+result);
int result2 = before + (int)rise;
System.out.println("今年苹果笔记本销售额为: "+result2); //精度丢失
int result3 = (int)(before + rise);
System.out.println("今年苹果笔记本销售额为: "+result3); //精度丢失
}
}
public class CalcAvg {
public static void main(String[] args){
double firstArg = 81.29;
double secondArg;
int rise = 2;
//自动类型转换：小范围-->大范围
//int 和 double运算，结果自动提升为double
secondArg = firstArg + rise;
System.out.println("第二次平均分为: "+secondArg);
}
}
运算符
import java.time.format.SignStyle;
public class CalcSymbol {
public static void main(String[] args){
// /取商 %取余
int num1 = 5;
int num2 = 2;
System.out.println(num1/num2); //商2
System.out.println(num1%num2); //余1
//自加++ 自减--
//++或--在变量前，先自加后自减运算，再使用
//反之，先使用完变量，再自加或者自减
// System.out.println(++num1); //6: num1 = num1 + 1
// System.out.println(--num2); //1 num2 = num2 - 1
// System.out.println(num1); //6
// System.out.println(num2); //1
System.out.println(num1++); //6: num1 = num1 + 1
System.out.println(num2--); //1 num2 = num2 - 1
System.out.println(num1); //6
System.out.println(num2); //1
//符合运算符
System.out.println("-----------------------");
int num3 = 5;
num3 += 2;
System.out.println(num3);
System.out.println("-----------------------");
double num4 = 5;
double num5 = 2;
System.out.println(num4/num5); //2.5
System.out.println(num4%num5); //1.0
}
}
逻辑判断
import java.util.Scanner;
public class LuckyCard {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("请输入您的四位会员卡号: ");
int no = input.nextInt();
//分解数字8645
int geWei = no % 10;
System.out.print("会员卡号的各位数字: 个位" + geWei);
int shiWei = no / 10 % 10;
System.out.print("十位" + shiWei);
int baiWei = no / 100 % 10;
System.out.print("百位" + baiWei);
int qianWei = no / 1000 % 10;
System.out.print("千位" + qianWei);
//计算数字之后
int sum = geWei + shiWei + baiWei + qianWei;
System.out.println("会员卡号后四位数字之和为: " + sum);
//判断和是否大于20
// String info = (sum<=20) ? "谢谢参与" : "恭喜卡号"+no+"的会员，您中了Iphone一部!";
// System.out.println(info);
//会员卡号百位数=系统随机数(0~10,不包括10)
int random = (int)(Math.random()*10);
// System.out.println(random);
if(baiWei==random){
System.out.println("恭喜会员"+no+"获得了精美礼品一份! ");
}else{
System.out.println("会员"+no+"感谢参与! ");
}
}
}
三目运算符
import java.util.Scanner;
public class IsEven {
//条件表达式判断是否为偶数 三目运算符
public static void main(String[] args){
Scanner input = new Scanner(System.in);
System.out.print("请输入一个非0的数字: ");
int num = input.nextInt();
String reuslt = (num%2==0) ? "偶数" : "奇数";
System.out.println(num+"是"+reuslt);
}
}
选择结构
IF语句
import com.sun.org.apache.xpath.internal.objects.XString;
import java.util.Scanner;
public class RunningMatch {
public static void main(String[] args){
Scanner input = new Scanner(System.in);
System.out.print("请输入跑步成绩(s): ");
double score = input.nextDouble();
//成绩判断
if(score<10){
//分组
System.out.print("请输入性别: ");
String sex = input.next();
if(sex.equals("男")){
System.out.println("进入男子组决赛!");
}else if(sex.equals("女")){
System.out.println("进入女子组决赛!");
}else{
System.out.println("性别输入不正确!");
}
}else{
System.out.println("淘汰!");
}
}
}
Case Switch语句
import java.util.Scanner;
public class Complete {
public static void main(String[] args){
Scanner input = new Scanner(System.in);
System.out.print("请输入比赛名次: ");
int rank = input.nextInt();
switch (rank) { //表达式内数据类型只能是int,short,byte,char,枚举类型String; 不能是double!!!!
case 1:
System.out.println("参加麻省理工大学计算机学院组织1个月的夏令营");
break;
case 2:
System.out.println("奖励惠普笔记本一部");
break;
case 3:
System.out.println("奖励移动硬盘一部");
break;
default:
System.out.println("没有任何奖励");
break;
}
}
}
循环结构
while循环
public class PrintExam {
public static void main(String[] args){
//打印试卷份数
int count = 1;
while(count<=50){
System.out.println("打印第"+count+"份试卷");
count++;
}
}
}
import java.util.Scanner;
public class StudyList {
public static void main(String[] args){
String answer;
Scanner input = new Scanner(System.in);
System.out.print("合格了吗？(y/n) ");
answer = input.next();
while(!"y".equals(answer)){
System.out.println("Do...");
//每次执行完需要再验证是否合格，保证能跳出循环
System.out.print("合格了吗？(y/n) ");
answer = input.next();
}
//合格时跳出循环：
System.out.println("完成!");
}
}
Do while循环
import java.util.Scanner;
public class DoWhileDemo {
public static void main(String[] args){
Scanner input = new Scanner(System.in);
String answer = ""; //标识是否为合格
do{
System.out.println("执行!");
System.out.print("合格了吗？(y/n) ");
answer = input.next();
}while(!answer.equals("y"));
//跳出循环后后执行
System.out.println("完成!");
}
}
for循环
public class PrintNums {
public static void main(String[] args){
//while
// int i = 1;
// while(i<=100){
// System.out.println(i);
// i++;
// }
//for
for(int i=1;i<=100;i++){
System.out.println(i);
}
}
}
import java.util.Scanner;
public class SumTable {
public static void main(String[] args){
int i,j;
Scanner input = new Scanner(System.in);
System.out.print("请输入一个值:");
int num = input.nextInt();
for(i=0,j=num; i<num; i++,j--){
System.out.println(i+"+"+j+"="+(i+j));
}
}
}
多重循环
public class PrintRectangle {
public static void main(String[] args){
//矩形
for (int i=1; i<=5; i++) {
for (int j = 1; j <= 5; j++) {
System.out.print("*");
}
System.out.println();
}
//平行四边形
for (int i=1; i<=5; i++){
for (int j=1;j<=5-i; j++) {
//输出每行的空格 5-i
int space = 5 -i;
System.out.print(" ");
}
for (int j=1;j<=5; j++) {
System.out.print("*");
}
System.out.println();
}
//等腰三角形
for (int i=1; i<=5; i++){
for (int j=1;j<=5-i; j++) {
//输出每行的空格 5-i
int space = 5 -i;
System.out.print(" ");
}
for (int j=1; j<=2*i-1; j++){
System.out.print("*");
}
System.out.println();
}
}
}
import java.util.Scanner;
public class PrintTrangleNums {
public static void main(String[] args) {
//等腰三角形
Scanner input = new Scanner(System.in);
System.out.print("多少行数字？ ");
int num = input.nextInt();
for (int i=1; i<=num; i++) {
for (int j = 1; j <= num - i; j++) {
//输出每行的空格 5-i
System.out.print(" ");
}
for (int j = 1; j <= 2 * i - 1; j++) {
System.out.print(i);
}
System.out.println();
}
}
}
//九九乘法表
public class PrintMultiTable {
public static void main(String[] args) {
for(int a=1; a<=9; a++){
for(int b=1; b<=a; b++){
System.out.print(a+"*"+b+"="+(a*b)+" ");
}
System.out.println();
}
}
}
break continue
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