//列印正三角
public class helloworld {
    public static void main(String[] args) {
        String cell="*";
        String space=" ";
        for (int lines=1; lines<=9; lines++) {
            // 只有偶數時才打印
            if (lines%2==0) {
                // 列印空格
                for (int spaces=1; spaces<=(9-lines)/2
 
; spaces++) {
                    System.out.print(space);
                }
                // 列印三角
                for (int cells=1; cells<=lines; cells++) {
                    System.out.print(cell);
                }
                // 列印空格
                for (int spaces=1; spaces<=(9-lines)/2
 
; spaces++) {
                    System.out.print(space);
                }
                System.out.println("");
            }
        }
    }
}

// 列印倒三角
public class helloworld {
    public static void main(String[] args) {
        String cell="*";
        String space=" ";
        for (int lines=9
 
; lines>=1; lines--) {
            // 只有偶數時才打印
            if (lines%2==0) {
                // 列印空格
                for (int spaces=1; spaces<=(9-lines)/2; spaces++) {
                    System.out.print(space);
                }
                // 列印三角
                for (int cells=1; cells<=lines; cells++) {
                    System.out.print(cell);
                }
                // 列印空格
                for (int spaces=1; spaces<=(9-lines)/2; spaces++) {
                    System.out.print(space);
                }
                System.out.println("");
            }
        }
    }
}

// 列印乘法口訣
public class helloworld {
    public static void main(String[] args) {
        for (int lines=1; lines<=9; lines++) {
            for (int columns=1; columns<=lines; columns++) {
                System.out.print(columns+"*"+lines+"="+columns*lines+"\t");
            }
            System.out.println();
        }
    }
}

附上圖片: