如何使用Java PrintWriter将void类型方法的结果打印到文件中

Question

我正在为我的Java编程课程做练习，问题是这样的：

编写一个名为printTree的方法，根据传递给过程的高度值向文件输出一个星号三角形。在主方法中测试此方法。

• 例如，高度为3的三角形应输出到名为file14的文件：

我只是不知道如何将void返回写入到我在main方法中创建的文件中。除了FileWriter之外，我想尽量减少任何其他java.io方法的导入，但我们非常感谢您的帮助，谢谢。

import java.io.PrintWriter;
public class OutputToFile14 {
public static void main(String[] args) throws Exception{

//Creating PrintWriter
PrintWriter output = new PrintWriter("file14.txt");

//writing method output to file
output.write(printTree(4));

//saving file
output.close();
}
public static void printTree (int height) throws IOException{

for (int i = 0; i < height; i++) {
for (int j = 0; j < height; j++) {
if (j < i) {
System.out.print("*");
}
}
System.out.println();
}
} 
}

Answer 1

四个观察结果。System.out是PrintStream(您可以将PrintStream传递给您的方法(。try-with-Resources允许您消除显式close()调用。使用System.getProperty("user.home")可以直接写入主文件夹(这很方便(。并且在内部循环中使用j < i而不是if (j < i)。比如

public static void main(String[] args) throws Exception {
try (PrintStream output = new PrintStream(
new File(System.getProperty("user.home"), "file14.txt"))) {
printTree(output, 4);
}
}
public static void printTree(PrintStream out, int height) throws IOException {
for (int i = 0; i < height; i++) {
for (int j = 0; j < i; j++) {
out.print("*");
}
out.println();
}
}

此外，由于Java 11，

public static void printTree(PrintStream out, int height) throws IOException {
for (int i = 0; i < height; i++) {
out.println("*".repeat(i)); // You might want "*".repeat(1 + i)
}
}

Answer 2

你可以像这个一样解决它

import java.io.PrintWriter;
public class OutputToFile14 {
public static void main(String[] args) throws Exception{

//Creating PrintWriter
PrintWriter output = new PrintWriter("file14.txt");

//writing method output to file
output.write(printTree(4));

//saving file
output.close();
}
public static String printTree (int height) throws IOException{
String output = "";

for (int i = 0; i < height; i++) {
for (int j = 0; j < height; j++) {
if (j < i) {
System.out.print("*");
output += "*";
}
}
System.out.println();
output += "rn";
}
return output;
} 
}

这是一种有点丑陋的快速解决方法。

import java.io.PrintWriter;
public class OutputToFile14 {
public static void main(String[] args) throws Exception{

//Creating PrintWriter
PrintWriter output = new PrintWriter("file14.txt");

//writing method output to file
//output.write(printTree(4));
printTree(4, output);

//saving file
output.close();
}
public static void printTree (int height, PrintWriter pw) throws IOException{

for (int i = 0; i < height; i++) {
for (int j = 0; j < height; j++) {
if (j < i) {
System.out.print("*");
pw.write("*");
}
}
System.out.println();
pw.write("rn");
}
} 
}