public class StudentDemo { public static void main(String[] args) { Scanner in = new Scanner(System.in); //学生一 String stuNo1 = in.next(); String name1 = in.next(); double english1 = in.nextDouble(); double math1 = in.nextDouble(); double Java1 = in.nextDouble(); double testScore1 = in.nextDouble(); Student s1 = new StudentPT(stuNo1,name1,english1,math1,Java1,testScore1); System.out.println(s1.toString()); //学生二 //学生三 } } interface Student{ String toString(); double sum(); //计算总成绩 double testScore(); //计算评测成绩注：评测成绩取三门课程成绩的平均分(保留2位小数) } class StudentPT implements Student{ private String stuNo; private String name; private double english; private double math; private double Java; private double testScore; private double max; public StudentPT (String stuNo,String name,double english,double math,double Java,double testScore){ this.stuNo =stuNo; this.name = name; this.english = english; this.math = math; this.Java = Java; this.testScore = testScore(); } public double sum(){ return english + math + Java; } public double testScore(){ return sum() / 3; } public String toString(){ return "stuNo:" + stuNo + " name:" + name + " english:%.1f" + english + " math:%.1" + math + " Java:%.1" + Java + "\n" + "testScore:%.2" + testScore; } } 无输出

这段代码存在一些问题，其中 `toString()` 方法中的格式化字符串不正确，应该使用 `%f` 而不是 `%`。此外，在 `toString()` 方法中应该使用 `String.format()` 方法来进行字符串的格式化，而不是直接使用字符串拼接。下面是修改后的代码：

public class StudentDemo {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);

        // 学生一
        String stuNo1 = in.next();
        String name1 = in.next();
        double english1 = in.nextDouble();
        double math1 = in.nextDouble();
        double java1 = in.nextDouble();
        double testScore1 = in.nextDouble();
        Student s1 = new StudentPT(stuNo1, name1, english1, math1, java1, testScore1);
        System.out.println(s1.toString());

        // 学生二
        // 学生三
    }
}

interface Student {
    String toString();
    double sum(); // 计算总成绩
    double testScore(); // 计算评测成绩，取三门课程成绩的平均分（保留2位小数）
}

class StudentPT implements Student {
    private String stuNo;
    private String name;
    private double english;
    private double math;
    private double java;
    private double testScore;
    private double max;

    public StudentPT(String stuNo, String name, double english, double math, double java, double testScore) {
        this.stuNo = stuNo;
        this.name = name;
        this.english = english;
        this.math = math;
        this.java = java;
        this.testScore = testScore();
    }

    public double sum() {
        return english + math + java;
    }

    public double testScore() {
        return sum() / 3;
    }

    public String toString() {
        return String.format("stuNo:%s name:%s english:%.1f math:%.1f java:%.1f\ntestScore:%.2f", stuNo, name, english, math, java, testScore);
    }
}

在这个程序中，我们定义了一个 `Student` 接口来描述学生的基本信息和成绩情况，其中包括 `toString()`、`sum()` 和 `testScore()` 三个方法。然后我们又定义了一个 `StudentPT` 类来实现 `Student` 接口，其中包含了学生的具体信息和实现 `Student` 接口所需的方法。在 `main` 方法中，我们通过输入学生信息来创建 `StudentPT` 对象，并输出其信息。