例：向已存在的 99.txt 中輸出一個99乘法表

import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintStream;

public class NineNineMultiply {
	public static void main(String[] args) throws FileNotFoundException {

		PrintStream psOld = System.out; // 儲存原來的輸出路徑
		System.setOut(new PrintStream(new File("99.txt")));// 設定輸出重新定向到檔案

		for (int i = 1; i <= 9; i++) {
			for (int j = 1; j <= i; j++) {
				System.out.print(String.format("%2$d*%3$d=%1$-3d", i * j, i, j));
			}
			System.out.println();
		}
		System.setOut(psOld); // 恢復原來的輸出路徑
	}

}