嵌套循环问题/循环2次，并且在切换情况下也默认运行

Question

我对嵌套循环有疑问。每当我请求显示特定的数据类型时，它都会显示出来，但问题是。它总是使输出翻倍。我如何阻止它？ Else也显示了任何其他内容。我在此处搜索所有嵌套的解决方案，但是我的代码中没有看到类似的代码解决方案。或我的代码有任何相似答案。

注意：我是JAVA编程的新手，这是我的第一个项目，所以请耐心等待，并向我解释一切我做错了什么以及在哪里出现此错误/错误:)谢谢您

这里是代码

case '2':
            System.out.print("Enter Subject: ");
            SB = buff.readLine();

            File readSUB = new File("E:\\Onceng Files\\JAVA GROUP PROJECT\\subject.txt");
            File readN = new File("E:\\Onceng Files\\JAVA GROUP PROJECT\\name.txt");
            File readSN = new File ("E:\\Onceng Files\\JAVA GROUP PROJECT\\studNo.txt");
            File readSEC = new File("E:\\Onceng Files\\JAVA GROUP PROJECT\\section.txt");
            File readTD = new File ("E:\\Onceng Files\\JAVA GROUP PROJECT\\TimeDate.txt");
            Scanner scaSUB = new Scanner(readSUB);
            Scanner scaN = new Scanner(readN);
            Scanner scaSN = new Scanner(readSN);
            Scanner scaSEC = new Scanner(readSEC);
            Scanner scaT = new Scanner(readTD);
            while(scaSUB.hasNextLine()) {
                String s = scaSUB.nextLine();
                SUBJECT.add(s);
            }

            while(scaN.hasNextLine()) {
                String s = scaN.nextLine();
                NAME.add(s);
            }

            while(scaSN.hasNextLine()) {
                String s = scaSN.nextLine();
                STUDNO.add(s);
            }

            while(scaSEC.hasNextLine()) {
                String s = scaSEC.nextLine();
                SECTION.add(s);
            }

            while(scaT.hasNextLine()) {
                String s = scaT.nextLine();
                TIME.add(s);
            }

            System.out.println("Attendance List by SUBJECT: "+SB);
            System.out.println("SUBJECT\t\tNAME\t\t\tSTUDENT NO.\t\tTIME & DATE");
            for(int x=0;x<SUBJECT.size();x++) {
                if(SB.equals(SUBJECT.get(x))) {
                    System.out.println(SUBJECT.get(x)+"\t\t"+NAME.get(x)+"\t\t"+STUDNO.get(x)+"\t\t"+TIME.get(x));
                } else
                    System.out.println("No Record of "+SB+" Subject");
            }

            break;

这里是输出

    @#@#@#@#@ MENU @#@#@#@#@
[1] LOGIN ATTENDANCE
[2] SHOW ATTENDANCE BY SUBJECT
[3] SHOW ATTENDANCE BY SECTION
[4] SHOW ALL RECORD
Input Number: 2
Enter Subject: JAVA
Attendance List by SUBJECT: JAVA
SUBJECT     NAME            STUDENT NO.     TIME & DATE
No Record of JAVA Subject
No Record of JAVA Subject
No Record of JAVA Subject
JAVA        Saludaga Joshua     19-01297        Tue, 12/03/2019 18:02
JAVA        Pulano Hardhie      19-00900        Tue, 12/03/2019 18:02
JAVA        Tatoy Cherrylyn     19-00751        Tue, 12/03/2019 18:02

Answer 1

        for(int x=0;x<SUBJECT.size();x++) {
            if(SB.equals(SUBJECT.get(x))) {
                System.out.println(SUBJECT.get(x)+"\t\t"+NAME.get(x)+"\t\t"+STUDNO.get(x)+"\t\t"+TIME.get(x));
            } else
                System.out.println("No Record of "+SB+" Subject");
        }

以上应写为。

boolean found = false;
        for(int x=0;x<SUBJECT.size();x++) {
            if(SB.equals(SUBJECT.get(x))) {
                System.out.println(SUBJECT.get(x)+"\t\t"+NAME.get(x)+"\t\t"+STUDNO.get(x)+"\t\t"+TIME.get(x));
found =true;
            }

        }
if(!found)
  System.out.println("No Record of "+SB+" Subject");

希望这可以解决您的问题。