试试我这个代码，应该能答应出菱形来！
import javax.swing.JOptionPane;

public class PrintStar {
    public static void main(String[] args) {
        String number = JOptionPane.showInputDialog("Enter an integer!");

        int n = Integer.parseInt(number);
        String output = "打印图形为：" + "\n";
        for (int i = 1; i <= n; i++) {
            for (int k = 1; k <= n - i; k++)
                output += "   ";
            for (int j = 0; j <= i - 1; j++)
                output += "* ";
            for (int m = 1; m <= i - 1; m++)
                output += "* ";
            output += "\n";
        }
        for (int i = n; i >= 1; i--) {
            for (int k = 1; k <= n - i; k++)
                output += "   ";
            for (int j = 1; j <= i - 1; j++)
                output += "* ";
            for (int m = 1; m <= i; m++)
                output += "* ";
            output += "\n";
        }

        JOptionPane.showMessageDialog(null, output);
    }

}