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{
    "1": {
        "subject1": "MIS",
        "subject2": "DBMS",
        "subject3": "UML"
    "2": {
        "subject1": "ART",
        "subject2": "MATH",
        "subject3": "MUSIC"
    "3": {
        "subject1": "HISTORY",
        "subject2": "CHEMISTY",
        "subject3": "BIOLOGY"
}

package com.company;
import org.json.JSONArray;
import org.json.JSONObject;
import java.io.FileReader;
public class Main {
    public static void main(String[] args) {
        String json = "{\"1\": {\"subject1\": \"MIS\",\"subject2\": \"DBMS\",\"subject3\": \"UML\"},\"2\": {\"subject1\": \"ART\",\"subject2\": \"MATH\",\"subject3\": \"MUSIC\"},\"3\": {\"subject1\": \"HISTORY\",\"subject2\": \"CHEMISTY\",\"subject3\": \"BIOLOGY\"}}";
            JSONObject root = new JSONObject(json);
            for (int i = 0; i < root.length(); i++) {
                JSONArray subjects = root.getJSONArray(String.valueOf(i+1));
                for (int j = 0; j < subjects.length(); j++) {
                    JSONObject number = subjects.getJSONObject(j);
                    String s1 = number.getString("subject1");
                    String s2 = number.getString("subject2");
                    String s3 = number.getString("subject3");
                    System.out.println(s1+", "+ s2+", "+s3);
        }catch(Exception e){
            e.printStackTrace();
}

JSONArray subjects = root.getJSONArray("1");
JSONArray subjects = root.getJSONArray("2");
...

org.json.JSONException: JSONObject["1"] is not a JSONArray.
    at org.json.JSONObject.wrongValueFormatException(JSONObject.java:2694)
    at org.json.JSONObject.getJSONArray(JSONObject.java:777)
    at com.company.Main.main(Main.java:18)

MIS, DBMS, UML
ART, MATH, MUSIC
HISTORI, CHEMISTRY, BIOLOGY

try{
     JSONObject root = new JSONObject(json);
     for (int i = 0; i < 3; i++) {
        JSONObject Obj = root.getJSONObject(String.valueOf(i+1));
        String s1 = Obj.getString("subject1");
        String s2 = Obj.getString("subject2");
        String s3 = Obj.getString("subject3");
        System.out.println(s1+", "+ s2+", "+s3);
  }catch(Exception e){
            e.printStackTrace();
  }

try{
    JSONArray root = new JSONArray(json);
    for (int i = 0; i < root.length(); i++) {
       JSONObject Obj = root.getJSONObject(i);
       String s1 = Obj.getString("subject1");
       String s2 = Obj.getString("subject2");
       String s3 = Obj.getString("subject3");
       System.out.println(s1+", "+ s2+", "+s3);
}catch(Exception e){
  e.printStackTrace();
}

JSONArray subjects = root.getJSONArray(String.valueOf(i+1));

for (int j = 0; j < subjects.length(); j++) {}

    String json = "{\"1\": {\"subject1\": \"MIS\",\"subject2\": \"DBMS\",\"subject3\": \"UML\"},\"2\": {\"subject1\": \"ART\",\"subject2\": \"MATH\",\"subject3\": \"MUSIC\"},\"3\": {\"subject1\": \"HISTORY\",\"subject2\": \"CHEMISTY\",\"subject3\": \"BIOLOGY\"}}";
    try {
        JSONObject root = new JSONObject(json);
        for (int i = 0; i < root.length(); i++) {
            JSONObject number = root.getJSONObject(String.valueOf(i + 1));
            String s1 = number.getString("subject1");
            String s2 = number.getString("subject2");
            String s3 = number.getString("subject3");
            System.out.println(s1 + ", " + s2 + ", " + s3);

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