Splitiing a string array into multiple subarrays in java based on prefix-CodePudding

I have several string inputs(registration number of students) from the user and I have to store them into different arrays based on their year of studying and print the output. For example, if string begins with "18" i have to store it as a 4th year student. If it begins with "19" i have to store it as 3rd year student and so on.

    import java.util.Scanner;
public class reg {
    public static void main(String args[]){
    Scanner scan = new Scanner(System.in);
    System.out.println("Enter no of students");
    int n = scan.nextInt();
    scan.nextLine();
    String[] arr = new String[n];
    System.out.println("Enter registration numbers");
    for(int i = 0;i<n;i  ){
        arr[i]=scan.nextLine();

    }

    String[] arr1 = new String[n];
    String[] arr2 = new String[n];
    String[] arr3 = new String[n];
    String[] arr4 = new String[n];
    String[] arr5 = new String[n];


    for(int i = 0;i<n;i  ){
        if(arr[i].startsWith("18")){
            for(int j = 0;j<n;j  ){
                arr1[j] = arr[i];
            }
        }
        else if(arr[i].startsWith("19")){
            for(int j = 0;j<n;j  ){
                arr2[j] = arr[i];
            }
        }
        else if(arr[i].startsWith("20")){
            for(int j = 0;j<n;j  ){
                arr3[j] = arr[i];
            }
        }
        else if(arr[i].startsWith("21")){
            for(int j = 0;j<n;j  ){
                arr4[j] = arr[i];
            }
        }
        else{
            for(int j = 0;j<n;j  ){
                arr5[j] = arr[i];
            }
        }

    }
    System.out.println("4th year students are");
    for(int i = 0;i<n;i  ){
        System.out.println(arr1[i]);
        System.out.println();
    }
    System.out.println("3rd year students are");
    for(int i = 0;i<n;i  ){
        System.out.println(arr2[i]);
        System.out.println();
    }
    System.out.println("2nd year students are");
    for(int i = 0;i<n;i  ){
        System.out.println(arr3[i]);
        System.out.println();
    }
    System.out.println("1st year students are");
    for(int i = 0;i<n;i  ){
        System.out.println(arr4[i]);
        System.out.println();
    }

    }
    
}

The output I'm getting is just the last input matching my condition getting printed n times (no. of students input).

How can I solve this issue?

Edit :

Input and expected ouput :

No of students :

Enter registration numbers :

20ABC123

19ABC111

18ABC000

18ABC001

21ABX144

20ABX000

19ABC099

Expected Output: 4th year students are

18ABC000

18ABC001

3rd year students are

19ABC111

19ABC099

2nd year students are

20ABC123

20ABX000

1st year students are

21ABX144

CodePudding user response：

You need to introduce new 5 variable for keeping track of total student in each category so that you can put next student on next empty position in category.

Scanner scan = new Scanner(System.in);
System.out.println("Enter no of students");
int n = scan.nextInt();
scan.nextLine();
String[] arr = new String[n];
System.out.println("Enter registration numbers");
for(int i = 0;i<n;i  ){
    arr[i]=scan.nextLine();

}

String[] arr1 = new String[n];
String[] arr2 = new String[n];
String[] arr3 = new String[n];
String[] arr4 = new String[n];
String[] arr5 = new String[n];
int studntFirstYear = 0;
int studntSecondYear = 0;
int studntThirdYear = 0;
int studntForthYear = 0;
int studntElse = 0;


for(int i = 0;i<n;i  ){
    if(arr[i].startsWith("18")){
        arr1[studntForthYear] = arr[i];
        studntForthYear  ;
    }
    else if(arr[i].startsWith("19")){
        arr2[studntThirdYear] = arr[i];
        studntThirdYear  ;
    }
    else if(arr[i].startsWith("20")){
        arr3[studntSecondYear] = arr[i];
        studntSecondYear  ;
    }
    else if(arr[i].startsWith("21")){
        arr4[studntFirstYear] = arr[i];
        studntFirstYear  ;
    }
    else{
        arr5[studntElse] = arr[i];
        studntElse  ;
        
    }

}
System.out.println("4th year students are");
for(int i = 0;i<studntForthYear;i  ){
    System.out.println(arr1[i]);
    System.out.println();
}
System.out.println("3rd year students are");
for(int i = 0;i<studntThirdYear;i  ){
    System.out.println(arr2[i]);
    System.out.println();
}
System.out.println("2nd year students are");
for(int i = 0;i<studntSecondYear;i  ){
    System.out.println(arr3[i]);
    System.out.println();
}
System.out.println("1st year students are");
for(int i = 0;i<studntFirstYear;i  ){
    System.out.println(arr4[i]);
    System.out.println();
}