Java重开第一周(01-06) day01:环境搭建和Hello Worldday02:基本算术操作day03:基本if语句和函数调用day04:if应用-闰年判断day05:Switch操作day06:For循环操作day01:环境搭建和Hello Worldday02:基本算术操作day03:基本if语句和函数调用day04:if应用-闰年判断day05:Switch操作day06:For循环操作
day01:环境搭建和Hello World day02:基本算术操作 day03:基本if语句和函数调用 day04:if应用-闰年判断 day05:Switch操作 day06:For循环操作 day01:环境搭建和Hello World day02:基本算术操作
关于Java变量命名：
一般将方法和变量的标识符按照小驼峰来写，如变量tempFirsInt;
类名的标识符一般用大驼峰来写，如BasicOperations；
关于注释：
代码区域包括数据声明，数据初始化，数据操作三个部分，且用注释来说明功能。
例如：//Modulus表示取余操作
//Of main 表示main方法结束
运行结果
本题中将常用的取绝对值方法单独取出来，并且实现成一个方法。该方法用static修饰，表示该方法与类同时产生，此时不能通过对象的方式来调用此方法(在本类中中还没有new出一个对象)，这里其实用到了封装的思想。
package basic;
public class LeapYear {
public static void main(String[] args) {
//Test is LeapYear
int tempYear = 2021;
System.out.println("" + tempYear + " is ");
if (!isLeapYear(tempYear)) {
System.out.println("NOT");
}//Of if
System.out.println("a leap year.");
tempYear = 2000;
System.out.println("" + tempYear + " is ");
if (!isLeapYear(tempYear)) {
System.out.println("NOT");
}//Of if
System.out.println("a leap year.");
tempYear = 2100;
System.out.println("" + tempYear + " is ");
if (!isLeapYear(tempYear)) {
System.out.println("NOT");
}//Of if
System.out.println("a leap year.");
tempYear = 2004;
System.out.println("" + tempYear + " is ");
if (!isLeapYear(tempYear)) {
System.out.println("NOT");
}//Of if
System.out.println("a leap year.");
//Test isLeapYearV2
System.out.println("Now we use the second version.");
tempYear = 2021;
System.out.println("" + tempYear + " is ");
if (!isLeapYearV2(tempYear)) {
System.out.println("NOT");
}//Of if
System.out.println("a leap year.");
tempYear = 2000;
System.out.println("" + tempYear + " is ");
if (!isLeapYearV2(tempYear)) {
System.out.println("NOT");
}//Of if
System.out.println("a leap year.");
tempYear = 2100;
System.out.println("" + tempYear + " is ");
if (!isLeapYearV2(tempYear)) {
System.out.println("NOT");
}//Of if
System.out.println("a leap year.");
tempYear = 2004;
System.out.println("" + tempYear + " is ");
if (!isLeapYearV2(tempYear)) {
System.out.println("NOT");
}//Of if
System.out.println("a leap year.");
}//Of main
public static boolean isLeapYear(int paraYear)
{
if((paraYear%4==0&¶Year%100!=0)||paraYear%400==0)
{
return true;
}
else{
return false;
}//Of if
}//Of isLeapYear
public static boolean isLeapYearV2(int paraYear)
{
if(paraYear%4==0){
return false;
}else if(paraYear %400==0){
return true;
}else if(paraYear%100==0)
{
return false;
}
else{
return true;
}//Of if
}//Of isLeapYearV2
}//Of class LeapYear
根据百度：非整百年：能被四整除的年是闰年
整百年：能被四百整除的是闰年
根据条件进行if逻辑条件抽象
方式一：if((paraYear%40&¶Year%100!=0)||paraYear%4000)
{
return true;
}
else{
return false;
}//Of if
方式二： if(paraYear%40){
return false;
}else if(paraYear %4000){
return true;
}else if(paraYear%100==0)
{
return false;
}
else{
return true;
}//Of if
运行结果：
package basic;
public class SwitchStatement {
public static void main(String[] args) {
scoreTolevelTest();
}//Of main
public static char scoreTolevelTest(int paraScore) {
//E stands for error ,and F stands for fail.
char resultLevel = 'E';
//Divided by 10, the result ranges from 0 to 10
int tempDigitalLevel = paraScore / 10;
//The use of break is important.
switch (tempDigitalLevel) {
case 10:
case 9:
resultLevel = 'A';
break;
case 8:
resultLevel = 'B';
break;
case 7:
resultLevel = 'C';
break;
case 6:
resultLevel = 'D';
break;
case 5:
case 4:
case 3:
case 2:
case 1:
case 0:
resultLevel = 'F';
break;
default:
resultLevel = 'E';
}//Of switch
return resultLevel;
}//OF scoreToLevel
public static void scoreTolevelTest() {
int tempScore = 100;
System.out.println("Score "+tempScore+"to level is: "+scoreTolevelTest(tempScore));
tempScore=91;
System.out.println("Score "+tempScore+"to level is:"+scoreTolevelTest(tempScore));
tempScore=82;
System.out.println("Score "+tempScore+"to level is:"+scoreTolevelTest(tempScore));
tempScore=75;
System.out.println("Score "+tempScore+"to level is:"+scoreTolevelTest(tempScore));
tempScore=66;
System.out.println("Score "+tempScore+"to level is:"+scoreTolevelTest(tempScore));
tempScore=52;
System.out.println("Score "+tempScore+"to level is:"+scoreTolevelTest(tempScore));
tempScore=8;
System.out.println("Score "+tempScore+"to level is:"+scoreTolevelTest(tempScore));
tempScore=120;
System.out.println("Score "+tempScore+"to level is:"+scoreTolevelTest(tempScore));
}//OF scoretoLevelTest
}//of class SwitchStatement
switch相当与多个if else的作用，可以实现单个信息的多段区分判断，常用于分数评级等题目中，若分段比较多，使用switch比较方便。
switch用法重点：当case条件语句匹配后只有遇到break才会跳出switch作用域，
default是所有case的条件都不匹配的时候，执行此语句。
day06:For循环操作
package basic;
public class ForStatement {
public static void main(String[] args) {
forStatementTest();
}//Of main
public static void forStatementTest(){
int temN=10;
System.out.println("1 add to "+temN+" is "+addToN(temN));
temN=0;
System.out.println("1 add to "+temN+" is "+addToN(temN));
int tempStepLength=1;
temN=10;
System.out.println("1 add to "+temN+" with step length "+tempStepLength+" is:"+addToWithStepLength(temN,tempStepLength));
tempStepLength=2;
System.out.println("1 add to"+temN+" with step length "+tempStepLength+" is:"+addToWithStepLength(temN,tempStepLength));
}//Of forStatementTest
public static int addToN(int paraN) {
int resultSum = 0;
for (int i = 1; i <= paraN; i++) {
resultSum += i;
}//Of for i
return resultSum;
}//Of addToN
public static int addToWithStepLength(int paraN,int paraStepLength)
{
int resultSum=0;
for(int i=1;i<=paraN;i+=paraStepLength)
{
resultSum+=i;
}//Of for i
return resultSum;
}//Of addToWithsStepLength
}//of class ForStatement.
运行结果
for(初始化; 布尔表达式; 更新) {
//代码语句
}
注意两个方法的运算不相同
addToN():从1到N，步长为1进行计算
addToWithStepLength（）:从1到N,步长为指定的参数，即for循环里的更新操作不同。
Java增强for循环
for(数据类型 变量名 : 数组或者集合对象){
//循环体，变量即元素
}
int[] numArray = { 1, 2, 3, 4, 5, 6 };
for (int i : numArray) {
System.out.print(i);
}
//结果会是123456
关于增强for循环的使用
link.
