英文:
How to format multiplication table into 4 rows and columns respectively and test for even number multiplication table between 1 and 9?
问题
这是我根据外部视频教程尝试的代码，但在格式方面没有得到预期的输出。
public class Lab3Class {
public static void main(String[] args) {
// TODO Auto-generated method stub
int table = 1;
while(table < 10) {
int i = 1;
while(i <= 10)
{
System.out.println(table + " * " + i + " = " + (table * i));
i++;
}
System.out.println(" ");
table++;
}
}
}
英文:
This is the code I atempted with the guide of external video which didnt cover expected output in terms of formatting
public class Lab3Class {
public static void main(String[] args) {
// TODO Auto-generated method stub
int table = 1;
while(table<10) {
int i = 1;
while(i<=10)
{
System.out.println(table+ " * "+i+" = "+(table*i));
i++;
}
System.out.println(" ");
table++;
}
}
}
答案1
得分: 0
你只是缺少了对偶数的检查，即 `if (table % 2 == 0)`。
public class Main {
public static void main(String[] args) {
int table = 1;
while (table < 10) {
if (table % 2 == 0) {
int i = 1;
while (i <= 10) {
System.out.println(table + " * " + i + " = " + (table * i));
i++;
}
}
System.out.println();
table++;
}
}
}
或者，你可以从 2 开始，并在每次迭代中将其增加 2，如下所示：
public class Main {
public static void main(String[] args) {
int table = 2;
while (table < 10) {
int i = 1;
while (i <= 10) {
System.out.println(table + " * " + i + " = " + (table * i));
i++;
}
System.out.println();
table += 2;
}
}
}
如果你需要以表格形式打印输出，可以按以下方式编写循环：
public class Main {
public static void main(String[] args) {
for (int line = 1; line <= 10; line++) {
for (int i = 2; i <= 10; i += 2) {
System.out.print(i + "*" + line + "=" + (i * line) + "\t");
}
System.out.println();
}
}
}
输出结果：
2*1=2 4*1=4 6*1=6 8*1=8 10*1=10
2*2=4 4*2=8 6*2=12 8*2=16 10*2=20
2*3=6 4*3=12 6*3=18 8*3=24 10*3=30
2*4=8 4*4=16 6*4=24 8*4=32 10*4=40
2*5=10 4*5=20 6*5=30 8*5=40 10*5=50
2*6=12 4*6=24 6*6=36 8*6=48 10*6=60
2*7=14 4*7=28 6*7=42 8*7=56 10*7=70
2*8=16 4*8=32 6*8=48 8*8=64 10*8=80
2*9=18 4*9=36 6*9=54 8*9=72 10*9=90
2*10=20 4*10=40 6*10=60 8*10=80 10*10=100
如你所见，使用 for 循环的方式看起来更加清晰。不过，我建议你也练习使用 while 循环。一旦你更加自信，我还建议你使用 String::format 或 System.out.printf 进行更好的格式化。
这是一个非常小的数据集，但如果数据集很大，你可以通过减少 I/O 操作来提高性能。为此，你可以将结果附加到 StringBuilder 并在最后一次性打印出来。
public class Main {
public static void main(String[] args) {
StringBuilder sb = new StringBuilder();
for (int line = 1; line <= 10; line++) {
for (int i = 2; i <= 10; i += 2) {
sb.append(i).append('*').append(line).append('=').append(i * line).append('\t');
}
sb.append('\n');
}
System.out.println(sb);
}
}
<details>
<summary>英文:</summary>
You are just missing a check for even numbers i.e. `if (table % 2 == 0)`.
public class Main {
public static void main(String[] args) {
int table = 1;
while (table < 10) {
if (table % 2 == 0) {
int i = 1;
while (i <= 10) {
System.out.println(table + " * " + i + " = " + (table * i));
i++;
}
}
System.out.println();
table++;
}
}
}
**Alternatively,** you can start table with `2` and increment it by 2 in each iteration as follows:
public class Main {
public static void main(String[] args) {
int table = 2;
while (table < 10) {
int i = 1;
while (i <= 10) {
System.out.println(table + " * " + i + " = " + (table * i));
i++;
}
System.out.println();
table += 2;
}
}
}
If you need to print it in a tabular structure, you can write the loops as follows:
public class Main {
public static void main(String[] args) {
for (int line = 1; line <= 10; line++) {
for (int i = 2; i <= 10; i += 2) {
System.out.print(i + "*" + line + "=" + (i * line) + "\t");
}
System.out.println();
}
}
}
**Output:**
2*1=2 4*1=4 6*1=6 8*1=8 10*1=10
2*2=4 4*2=8 6*2=12 8*2=16 10*2=20
2*3=6 4*3=12 6*3=18 8*3=24 10*3=30
2*4=8 4*4=16 6*4=24 8*4=32 10*4=40
2*5=10 4*5=20 6*5=30 8*5=40 10*5=50
2*6=12 4*6=24 6*6=36 8*6=48 10*6=60
2*7=14 4*7=28 6*7=42 8*7=56 10*7=70
2*8=16 4*8=32 6*8=48 8*8=64 10*8=80
2*9=18 4*9=36 6*9=54 8*9=72 10*9=90
2*10=20 4*10=40 6*10=60 8*10=80 10*10=100
As you can see, it looks cleaner by using a `for` loop. However, I recommend you also practice it with a `while` loop. Once you gain more confidence, I also recommend you use [String::format][1] or `System.out.printf` for better formatting.
This is a very small data set but if the dataset is huge, you can improve the performance by reducing the I/O operation. For this, you can append the result to a `StringBuilder` and print it just once at the end.
public class Main {
public static void main(String[] args) {
StringBuilder sb = new StringBuilder();
for (int line = 1; line <= 10; line++) {
for (int i = 2; i <= 10; i += 2) {
sb.append(i).append('*').append(line).append('=').append(i * line).append('\t');
}
sb.append('\n');
}
System.out.println(sb);
}
}
[1]: https://docs.oracle.com/javase/7/docs/api/java/lang/String.html#format(java.lang.String,%20java.lang.Object...)
</details>
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