Swtich
当一个case 成立，从这个case向后穿透所有case，包括default代码，直到结束，或者遇到break跳出
只能判断:
byte/short/char/int
Enum
Jdk1.7之后可以判断 String
只能是字面值不能是变量或表达式
百分制转五档分制
package day0304;
import java.util.Scanner;
public class Test1 {
public static void main(String[] args) {
System.out.print("输入百分数:");
int i = new Scanner(System.in).nextInt();
f(i);
}
private static void f(int i) {
if (i < 0 || i > 100) {
System.out.println("输入分数有误");
return;
}
String r = "";
switch (i / 10) {
case 10:
case 9:
r = "A";
break;
case 8:
case 7:
r = "B";
break;
case 6:
r = "C";
break;
case 5:
case 4:
case 3:
case 2:
r = "E";
break;
case 1:
case 0:
r = "F";
break;
}
System.out.println("五分制:" + r);
}
}
for循环
for(变量赋值; 执行条件; 变量修改) {
…
}
例如打印1到10：
for(int i=1; i<=10; i++) {
System.out.println(i);
}
package day0305;
public class Test1 {
public static void main(String[] args) {
f1();
f2();
f3();
f4();
f5();
}
private static void f1() {
for(int i=1;i<=10;i++) System.out.print(i+",");
}
private static void f2() {
for(int i=10;i>=1;i--) System.out.print(i+",");
}
private static void f3() {
for(int i=2;i<=10;i+=2) System.out.print(i+",");
}
private static void f4() {
for(int i=8;i<=88888888;i=i*10+8) System.out.print(i+",");
}
private static void f5() {
//死循环
for(int i=1;;i++) System.out.println(i);
}
}
求Π的值
Π/2=1/1-1/3+1/5-1/7+1/9…
package day0305_求Π值;
import java.util.Scanner;
public class Test1 {
public static void main(String[] args) {
System.out.print("请输入计算次数:");
int i = new Scanner(System.in).nextInt();
f(i);
}
private static void f(int i) {
double result = 0;
for (int n = 1, a = 1, b = 1; n <= i; n++, a *= -1, b += 2) {
result += (double) a / b;
}
System.out.println(result * 4);
}
}
鸡兔同笼
鸡兔共35只,有94只脚,问鸡和兔各有几只?
package day0304;
public class Test1 {
public static void main(String[] args) {
for (int j = 0, t = 35; j <= 35; j++, t--) {
if (j * 2 + t * 4 == 94) System.out.println("鸡:" + j + "兔:" + t);
}
}
}
质数
输入一个值判断是否是质数
package day0308;
import java.util.Scanner;
public class Test1 {
public static void main(String[] args) {
System.out.print("请输入一个质数:");
int i = new Scanner(System.in).nextInt();
f(i);
}
private static void f(int i) {
double max = Math.sqrt(i) + 1;
for (int j = 2; j < max; j++) {
if (i % j == 0) {
System.out.println("不是质数");
return;
}
}
System.out.println("是质数");
}
}
循环嵌套
package day0305;
import java.util.Scanner;
public class Test2 {
public static void main(String[] args) {
f1();
System.out.print("请输入要打印的行数:");
int i = new Scanner(System.in).nextInt();
f2(i);
System.out.print("请输入要打印的行数:");
i = new Scanner(System.in).nextInt();
f3(i);
}
private static void f1() {
for (int i = 1; i <= 3; i++) {
for (char j = 'a'; j <= 'c'; j++)
System.out.println(i + "," + j);
}
}
private static void f2(int i) {
for (int n = 1; n <= i; n++) {
for (int nn = 1; nn <= i; nn++) System.out.print("*");
System.out.println();
}
}
private static void f3(int i) {
for (int n = 1; n <= i; n++) {
for (int nn = 1; nn <= n; nn++) System.out.print("*");
System.out.println();
}
}
}