How to access JSON values in Apex

 String data = '{"Technology":"Salesforce","countries":[{"countryName":"India","states":[{"AP":"AndhraPradesh","TS":"Telangana","KA":"Karnataka"}]},{"countryName":"USA","states":[{"TS":"Texas","VA":"Virginia","WA":"Washington"}]}]}';

Map<String, Object> mapData = (Map<String, Object>) JSON.deserializeUntyped(data);

//get the Technology value

String technVal = String.valueOf(mapData.get('Technology'));

system.debug('==Technology value==='+technVal);

//output: Salesforce

//get the countries list

List<Object> countriesList = (List<Object>) mapData.get('countries');

system.debug('==countriesList=='+countriesList);

//output: ({countryName=India, states=({AP=AndhraPradesh, KA=Karnataka, TS=Telangana})}, {countryName=USA, states=({TS=Texas, VA=Virginia, WA=Washington})})



//get the first record from the countriesList

system.debug('==First record=='+countriesList[0]);

//output: {countryName=India, states=({AP=AndhraPradesh, KA=Karnataka, TS=Telangana})}



//get the second record from the countriesList

system.debug('==Second record=='+countriesList[1]);

//output: {countryName=USA, states=({TS=Texas, VA=Virginia, WA=Washington})}



//get the key and value of the first record

Map<String, Object> firstRecord = (Map<String, Object>) countriesList[0];

String countryName = String.valueOf(firstRecord.get('countryName'));

system.debug('==FirstRecord CountryName=='+countryName);

//output: India



//get the states value based on the key

List<Object> statesList = (List<Object>) firstRecord.get('states');

Map<String, Object> mapstatesData = (Map<String, Object>) statesList[0];

String apStateVal = String.valueOf(mapstatesData.get('AP'));

System.debug('==AP state value =='+apStateVal);

//output: AndhraPradesh