第二章

1、常量的定义及应用

public class FinalDemo{

public static void main(String[] args){
final double PI = 3.14;
int r = 8;
System.out.println("圆的面积是："+PI*r*r);
System.out.println("圆的周长是："+PI*r*2);
}

}

2、boolean 、关系运算符类型运算

public class OperationDemo
{
public static void main(String[] args){
int a = 2;
int b = 3;
boolean c = a==b;
boolean d = a>b;
System.out.println(a==b);
System.out.println(a!=b);
System.out.println(a>b);
System.out.println(a<b);
System.out.println("===========");
System.out.println(c);
System.out.println(d);
a*=b;
a%=b;
System.out.println(a);
System.out.println(b);
}
}

3、Scanner扫描

import java.util.*;
public class DoubleDemo{
public static void main(String[] args){
// Scanner 扫描输入
System.out.print("请输入一个四位数：");
Scanner sc = new Scanner(System.in);
int a = sc.nextInt();
// 取得个 十 百 千 位  数字
int g = a/1%10;
int s = a/10%10;
int b = a/100%10;
int q = a/1000%10;
// 加5余10  取得数字
g = (g+5)%10;
s = (s+5)%10;
b = (b+5)%10;
q = (q+5)%10;
// 换位后地加密后数字
System.out.println("加密后是："+(g*1000+s*100+b*10+q));
}
}

4、i++及++i的运算

public class StringDemo
{
public static void main(String[] args){
int i = 2;
//i++;
//++i;
int a = i++;
int b = ++i;
System.out.println(a);
System.out.println(b);
System.out.println(i);


}
}