java - 在Java输出中插入空行

我有一些代码，我想打印出其中有学生的所有班级清单。我希望此列表按class_id排序，并且我希望每个不同的类之间都有一个空格。例如：

100 Math Jon Doe
100 Math Tina Lee
100 Math Sally

122 Science Tom Edison
122 Science Jon Frankin

现在，代码可以正确打印了，除了没有空格分隔各类。

我知道错误在这里：

while(!"class_id".equals("class_id")) {
                    System.out.println("\n");

                }

只是不确定我在做什么错。

static void listAllClasses() {
        System.out.println("\nClasses With Enrollment\n");
        try {
            con = DriverManager.getConnection("jdbc:mysql://localhost:3306/ClassSelector?autoReconnect=true&useSSL=false", "", "");
            String totalEnroll = ("SELECT * FROM ClassSelector.student_x_class ORDER BY class_id");
            myStmt = con.prepareStatement(totalEnroll);

            rs = myStmt.executeQuery(totalEnroll);
            while (rs.next()) {
                String totalEnrollment = rs.getString("class_id") + "\t" + rs.getString("class_name") + "\t"  + rs.getString("student_id") + "\t" + rs.getString("student_name");
                while(!"class_id".equals("class_id")) {
                    System.out.println("\n");

                }
                System.out.println(totalEnrollment);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

最佳答案

尝试这个 ：

static void listAllClasses() {
        String currentClassId ="";
        String oldClassId = "";
        System.out.println("\nClasses With Enrollment\n");
        try {
            con = DriverManager.getConnection("jdbc:mysql://localhost:3306/ClassSelector?autoReconnect=true&useSSL=false", "", "");
            String totalEnroll = ("SELECT * FROM ClassSelector.student_x_class ORDER BY class_id");
            myStmt = con.prepareStatement(totalEnroll);

            rs = myStmt.executeQuery(totalEnroll);
            while (rs.next()) {
                currentClassId = rs.getString("class_id");
                String totalEnrollment = rs.getString("class_id") + "\t" + rs.getString("class_name") + "\t"  + rs.getString("student_id") + "\t" + rs.getString("student_name");
                while(currentClassId != null && oldClassId != null && !currentClassId.equals(oldClassId)) {
                    System.out.println("\n");

                }
                oldClassId = currentClassId;
                System.out.println(totalEnrollment);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

关于java - 在Java输出中插入空行，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/36088483/