输出三角形
class ForForTest{
public static void main(String[] args){
for(int i = 1; i<= 5; i++){ //控制行数
for(int j = 1; j <= i; j++){ //控制列数
System.out.print("*");
}
System.out.println();
}
for(int i = 1; i<= 4; i++){
for(int j = 1; j<= 5-i; j++){
System.out.print("*");
}
System.out.println();
}
}
}
结果:
*
**
***
****
*****
****
***
**
*
九九乘法表
class NineNineTable{
public static void main(String[] args){
for(int i = 1; i <= 9; i++){
for(int j = 1; j <= i; j++){
System.out.print( i + " * " + j + " = " + i*j + " ");
}
System.out.println();
}
}
}
结果:
1 * 1 = 1
2 * 1 = 2 2 * 2 = 4
3 * 1 = 3 3 * 2 = 6 3 * 3 = 9
4 * 1 = 4 4 * 2 = 8 4 * 3 = 12 4 * 4 = 16
5 * 1 = 5 5 * 2 = 10 5 * 3 = 15 5 * 4 = 20 5 * 5 = 25
6 * 1 = 6 6 * 2 = 12 6 * 3 = 18 6 * 4 = 24 6 * 5 = 30 6 * 6 = 36
7 * 1 = 7 7 * 2 = 14 7 * 3 = 21 7 * 4 = 28 7 * 5 = 35 7 * 6 = 42 7 * 7 = 49
8 * 1 = 8 8 * 2 = 16 8 * 3 = 24 8 * 4 = 32 8 * 5 = 40 8 * 6 = 48 8 * 7 = 56 8 * 8 = 64
9 * 1 = 9 9 * 2 = 18 9 * 3 = 27 9 * 4 = 36 9 * 5 = 45 9 * 6 = 54 9 * 7 = 63 9 * 8 = 72 9 * 9 = 81
求100以内的质数
class PrimeNumberTest{
public static void main(String[] args){
boolean isFlag = true; //标识i是否被j除尽，一旦除尽，修改其值
for(int i = 2; i <= 100; i++){ //遍历100以内的自然数
for(int j =2; j < i; j++){
if(i % j == 0){
isFlag = false;
break;
}
}
if(isFlag == true){
System.out.println(i);
}
//重置 isFlag
isFlag = true;
}
}
}
结果:
2
3
5
7
11
13
17
19
23
29
31
37
41
43
47
53
59
61
67
71
73
79
83
89
97
求100000以内的质数个数
class PrimeNumberTest2{
public static void main(String[] args){
boolean isFlag = true; //标识i是否被j除尽，一旦除尽，修改其值
int count = 0; //质数的个数
//获取当前时间距离 1970-01-01 00:00:00 的毫秒数
long start = System.currentTimeMillis();
for(int i = 2; i <= 100000; i++){ //遍历100000以内的自然数
for(int j =2; j <= Math.sqrt(i); j++){
if(i % j == 0){
isFlag = false;
break;
}
}
if(isFlag == true){
//System.out.println(i);
count++;
}
//重置 isFlag
isFlag = true;
}
//获取当前时间距离 1970-01-01 00:00:00 的毫秒数
long end = System.currentTimeMillis();
System.out.println("质数的个数为: " + count);
System.out.println("所花费的时间为: " + (end - start));
}
}
class PrimeNumberTest3{
public static void main(String[] args){
int count = 0; //质数的个数
//获取当前时间距离 1970-01-01 00:00:00 的毫秒数
long start = System.currentTimeMillis();
klvchen:for(int i = 2; i <= 100000; i++){ //遍历100000以内的自然数
for(int j =2; j <= Math.sqrt(i); j++){
if(i % j == 0){
continue klvchen;
}
}
//能执行到此步骤的，都是质数
count++;
}
//获取当前时间距离 1970-01-01 00:00:00 的毫秒数
long end = System.currentTimeMillis();
System.out.println("质数的个数为: " + count);
System.out.println("所花费的时间为: " + (end - start));
}
}