public class qwe {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
int r=2;
double π=3.14;
System.out.println(r*r*π);
}
}
![](https://img2020.cnblogs.com/blog/2320047/202103/2320047-20210314180051244-1856172708.png)
public class five {
public static void main(String[] args){
int a=123;
int b,c,d,e,sum;
b=a/1000;
c=a/100%10;
d=a/10%10;
e=a%10;
sum=b+c+d+e;
System.out.println(sum);
}
}
![](https://img2020.cnblogs.com/blog/2320047/202103/2320047-20210314180140686-1130475717.png)
int a=5,b=8;
int c;
c=a;
a=b;
b=c;
System.out.println(a);
System.out.println(b);
![](https://img2020.cnblogs.com/blog/2320047/202103/2320047-20210314180307360-1679848149.png)
int a=12345,b;
b=a/100*100;
System.out.println(b);
![](https://img2020.cnblogs.com/blog/2320047/202103/2320047-20210314180338011-1690553034.png)
package zy2;
public class Test2 {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
int b,c,d,sum;
int a=456;
b=a/100;
c=a/10%10;
d=a%10;
sum=b+c+d;
System.out.println("结果为"+sum);
![](https://img2020.cnblogs.com/blog/2320047/202103/2320047-20210314180412859-1725953767.png)
package zy2;
public class Test2 {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
char a='F';
System.out.println((char)(a+32));
char b='g';
System.out.println((char)(b-32));
![](https://img2020.cnblogs.com/blog/2320047/202103/2320047-20210314180451239-2132300777.png)