2019独角兽企业重金招聘Python工程师标准>>> 
1、true/false
Java中不允许将一个数字作为布尔值使用。
if(a)//不允许,若a为非布尔值
//可以转化为
if(a != 0)2、“else if”并非是一个新的关键字，仅仅是一个else后面紧跟if语句。
package Fourth;
/*随机输出25个int型随机数，对每一个随机数使用if-else语句将其分类为大于、小于、等于紧随它生成的随机数*/
import java.util.Random;
public class IfElseNextInt {
public static void main(String[] args){
int[] a = new int[25];
int count1 = 0,count2 = 0,count3 = 0;
Random random = new Random();
for(int i = 0;i<25;i++){
a[i] = random.nextInt();
System.out.print(a[i]+" ");
}
System.out.println(" ");
for(int j = 0; j<24; j++){
if(a[j] < a[j+1]){
System.out.println(a[j]+"小于"+a[j+1]);
count1++;
}else if(a[j]< a[j+1]){
System.out.println(a[j]+"等于"+a[j+1]);
count2++;
}else{
System.out.println(a[j]+"大于"+a[j+1]);
count3++;
}
}
System.out.println("count1 = "+count1);
System.out.println("count2 = "+count2);
System.out.println("count3 = "+count3);
}
}/*Outputs:
-1354703007 1805422196 -1297880545 1793371722 -234103217 -833903965 -1176050239 1179914159 1647912769 -917685928 -645989902 522511923 -1215204011 1866894430 -998138732 716269013 -469080041 -1602332390 -1863176595 -160521188 -1280051709 -2121712965 1478433613 866361195 -1817443512
-1354703007小于1805422196
1805422196大于-1297880545
-1297880545小于1793371722
1793371722大于-234103217
-234103217大于-833903965
-833903965大于-1176050239
-1176050239小于1179914159
1179914159小于1647912769
1647912769大于-917685928
-917685928小于-645989902
-645989902小于522511923
522511923大于-1215204011
-1215204011小于1866894430
1866894430大于-998138732
-998138732小于716269013
716269013大于-469080041
-469080041大于-1602332390
-1602332390大于-1863176595
-1863176595小于-160521188
-160521188大于-1280051709
-1280051709大于-2121712965
-2121712965小于1478433613
1478433613大于866361195
866361195大于-1817443512
count1 = 10
count2 = 0
count3 = 14*///~3、Foreach
Java1.5以后新增的foreach语法
package Fourth;
import java.util.Random;
public class Foreach {
public static void main(String[] args){
Random random = new Random();
float[] a = new float[10];
for(int i = 0;i < 10; i++){
a[i] = random.nextFloat();
}
/**java1.5以后，此条语句定义了一个float型的x，继而将每一个
* 数组a的值赋给x*/
for(float x: a){
System.out.print(x+" ");
}
}
}/*Outputs:
0.32246327 0.59484965 0.20389026 0.70910615 0.31593043 0.6692021 0.4307089 0.36957538 0.87660265 0.8898278*/
package Fourth;
public class ToCharArray {
public static void main(String[] args){
String str = "IwanttobetrongandIwill";
/**String类的toCharArray()方法
* char[] java.lang.String.toCharArray()
* Converts this string to a new character array.*/
for(char x: str.toCharArray())
System.out.print(x+" ");
}
}/*Outputs:
I w a n t t o b e t r o n g a n d I w i l l */4、for
package Fourth;
/*输出100以内的素数*/
public class ForSuShu {
public static void main(String[] args){
/*int i, j;
for (i = 2; i <= 100; i++) {
for (j = 2; j < i; j++) {
if (i % j == 0)
break;//跳出内层循环
}
if (j >= i)
System.out.println(i);
}*/
boolean bool;
for (int i = 3; i < 100; i+=2) {
bool = true;
for (int j = 3; j <= Math.sqrt(i); j++) {
if (i % j == 0) {
bool = false;
break;
}
}
if (bool)
System.out.print(i + " ");
}
}
}/*Outputs:
3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97*/
package Fourth;
public class E10_Vampire {
public static void main(String[] args) {
int[] startDigit = new int[4];
int[] productDigit = new int[4];
for(int num1 = 10; num1 <= 99; num1++)
for(int num2 = num1; num2 <= 99; num2++) {
// Pete Hartley's theoretical result:
// If x·y is a vampire number then
// x·y == x+y (mod 9)
if((num1 * num2) % 9 != (num1 + num2) % 9)
continue;
int product = num1 * num2;
startDigit[0] = num1 / 10;
startDigit[1] = num1 % 10;
startDigit[2] = num2 / 10;
startDigit[3] = num2 % 10;
productDigit[0] = product / 1000;
productDigit[1] = (product % 1000) / 100;
productDigit[2] = product % 1000 % 100 / 10;
productDigit[3] = product % 1000 % 100 % 10;
int count = 0;
for(int x = 0; x < 4; x++)
for(int y = 0; y < 4; y++) {
if(productDigit[x] == startDigit[y]) {
count++;
productDigit[x] = -1;
startDigit[y] = -2;
if(count == 4)
System.out.println(num1 + " * " + num2
+ " : " + product);
}
}
}
}
} /*Outputs:
15 * 93 : 1395
21 * 60 : 1260
21 * 87 : 1827
27 * 81 : 2187
30 * 51 : 1530
35 * 41 : 1435
80 * 86 : 6880*/