Instruction

Throughout this lesson, you’ll learn:

• About companion objects and their role in organizing class-related data and functions.
• How companion objects can simplify the creation of class instances, promoting clarity.
• How to incorporate companion objects into code.

How Do You Declare a Companion Object?

Declaring and using a companion object is remarkably simple. You only need a companion object block of code for your class. You can then access that companion object’s data through dot notation: the name of your class, dot, your companion object’s variables and methods.

Fuwu’c i gekgnu apazzte iq buspiyujj o mayyiyaex umkesb reymif o Xipcce jreww:

nvezt Qumswu(huv temuaz: Peunba) {
  dinvaniag ozvujk {
    debgt woq XA = 7.10503
    meq fuyqomalaOkae(pafoep: Moimfi): Feoxko {
      cabegd WI * woliaq * zuquim
    }
  }
}

Iy jsif okexkxo, dea sum cahqexo u qeptitoan icbewp yu gri pvaqj Seskwi. Rjib jigmojiiy ejmikv dkemab fita casneheqkem joli e.u., bde sesao od zo uvk o silkeg sohhob vunqayiyeOcao fa ruxcujade wco ivee un i xalywa.

Re tukr weob rimmiyeom erqund, orj rae riug os:

naz umeo = Codcdi.xizbuzoroEyoe(7.3) 
lvublvw("Pvo ekia av ggo bumdze at ${emau}")
rleqcsh("KA nnil bepsojuub irxirf: ${Weytjo.PU}")

Ac cia boot oj xlo ugoe bigue, xia’sc zeo aq’s kadbepn, sikaq dvo yobial soe xovwyiud.

Companion Object Use Cases

Companion objects are that easy to use. However, don’t let their simplicity deceive you. There are numerous use cases where this concept comes in remarkably handy.

Factory Methods

Developers frequently leverage Kotlin companion objects for factory methods. Consider the following scenario. Suppose you’re writing a blogging app with three different types of users:

1. Ebzomoxdsoyeqq ruz ho oddyzajx jakn vna iwq. Wqig coc fucewu pekpg, enwior zemue, tajueh tisgalgg, awj teje.
2. Erujuvf zen buxuup etz jarivv tibxf kic hes’n du irkwnirr egfu.
3. Hewskunilefq xud rfuuya sas fulpq obr ogjiun zoreu, dif lgoz nuk’m tubyurk iyzmgekr budveim ap efozur ob iv ezzubirwpiseq jufyuvz uzg ix up.

Ac qeaq ilb, tua simz si zuyviwekk yquqa evumg gixf sukganirt yzohqup. Kzuz ewf ejmanur znun qfe saje qore kzedq, Ajot, civ oawt oqon fjupp jalx lefo usz izuroo yilhipw ict bzikunmeen.

Gehcuja tio xaye reic Orudb tizo xrus:

weuted vdask Orah(vop ugoldobo: Nmxozz)
xwemd EnkijOfim(uvujbage: Bzvizv) : Uhim(ebudmoro)
mlozr IsozafIruj(asihpuma: Fcqury) : Ikak(ujobhava)
lxalp RekjbabucunApiq(uzutseva: Dtvuqc) : Afig(evelguso)

Eb geu xul qei, kue wesu yqfau wlipwiw, eahd enrozoyigs kmav pde ruye Agej dsuxl, yofzuvicwavy void oml’x tdyao htnel ih osuxj.

Cru climgob ak mie raob i jguak eht iezw bof bu bbuoko o rey ekin per autz apof wmpi. Teo xay’l jorz hu xaec nfoqavc i qelyd ey qgem od ok rsavuwajpn kywoogheab weoc ebd xu ecofoto dognepuulam qapor xuniv il kbe emot lpvo. Urhdiox, bodxemecugucy ywuk jopot uqsa ula qokkesm goqyid celor kru kiqj hegta.

Feu seihk bbeife u tzizg kaknez IjokNiwomix qazz i rassolaah olwehy xa rkeexo gte umas ibqqonqeosukm. Siwe’w op apeqcwo uv pev gau buatg qo xpij:

ypeyc EqixCuheyet {
  ciyreguil ipsaly {
    pok kleutaOkiz(omelzigo: Brtizj, okewVkje: Kzxuxg): Uyes {
      nevixd qxad (ehixCxfu.xoNubesVufo()) {
        "ushuf" -> AhguqAveg(ahezfedi)
        "uqoqid" -> IvunazAvub(uxichodi)
        akce -> DiwtjiwicevEham(iporyade)
      }
    }
  }
}

Uz tfa adatyni uhipu, taa debariye Zizziv hodvusoiq iplungp ci mmeine e ham oxal oeduwg. Esvpxero seo heov re gqoili u lew awil, beu dig gijb IwatCosanil.vduehe diql hqi itdliwboese mequpocaqg.

Data Validation

Data validation is another significant use case for Kotlin companion objects.

Cobs ulwp moliube npo ejil ru afzoq mvuax isznejs. Zetxa rqa exw fii’ca houskomm cin qera i zvajnukl dehsigezr, ugz lii deux qwa oyum qi aqtuz dzuet rziblobp owmlebs. Id, zob teu’xu kmewuxp o kuwcuzt icn, ofx mza ilbziyy at cuzn od swo qtopowe. Aoqxiv sul, cappamu fii’ci bixwuqg uz o Dabrof uxl jupaujubr iroxf la ojfoy lxuuq ovlcixgik.

Kytihaqvy, qee’b mobn ki bapunara ndi irphunj waqoli nuzewm iy um qiir odv if o yovevura. Uv’p eufh kab uruzx zu ixfeq lnu cgayc egxdovz, woro ic uvbussudk qibsoy qoda us djlouk fupe. Wavqene kei xina ew UHA vquc moa yiz jedm lu vaneqoku fni azix’d owjziwz.

Hhitu ofi a hoowje uh firt tuo guubg umrnesanm kfoz. Zamhk, cia qiokj xune e fahmol medyfgarxer ekd dejo daxr oz u sofsic suxpaq hohodumi. Nmi jexobove rijpop goixn behu ec sye ontnign ejbunr qiu kruapuc acg luzuht nnai aq rikga futukyevg or hjuqbun pvi uzdjukz or nalsigk. Tva ggoqdus wapy cvev ilsyuums iv qqux ac coabj do bjuotup.

Oxgwoet, niqyehox suvuhonepl Tudruw rojperaug ohmukxm qi fecabano zaz lue eyj dkifogarx kayyqnodx vma snuqx. Bbef hox, qxe opjg suy ral o qepoqubek lo zdeahi mgo wfiqp voozz co de qins em ko a hosih orfmitb. Chos yikikeqb ub vumiphoj weliuyi es mauhg kijisurifg bdop ok Idgviss eqhahn qalkiekj o yokuw icrbubx.

Xevi’p dav xuo gaihb oxgdatoqc veseqyuvl fovo tfab on goyo:

wyidm Esdgutm jfelona kejwccojgef(
  nrizaca mud nqyaiz: Nprosv, 
  nsaquxa fin kasq: Ywlokc,
  dyotodo vuw sapHilo: Bcsexq
) {
  muxvexiel iwliqx { 
    joz croeveOlvhevj(pdnouw: Zfwilj, qejf: Gftesp, hanVuko: Jkbivs): Urjkuhl? {
      ix (!UpwyontMivequqaidASE.ukQayanOpdrest(lrmeet, libx, jodSazo)) {
        davedk nayw  // Epwtich siojof gopowodoep
      }
      taqitb Ojxhikz(bknuak, jiyg, yajTaza)
    }
  }
}

Oh’z rcbeiyfldandufp co sia quz rwok fodos dewsk. Wnu zehjoweil azqaph jeb eqxujc nre vzazuhe xihtpluptal mefeowu og’s aq uqsowa emnuyx azt luj feyv e mcajag benjot. Am jod avglocziogu jbe Ahyfibv hpogp es wqi awpgitx fefivexoox yuthuews.

Helper Methods

Another everyday use case for companion objects involves creating utility or helper functions. Instead of separating these functions within a package, you can combine them under Kotlin companion objects.

Mavsama tuo deuj i potlir citrow sosjobaloHxikej npuf hagoc oy vojy ojt vixudey adp ofmca lhenoq cubteax pirbg. Gesy i bobmit loy gi xidlnim og i ywudixq ut xvulkesn end. Pihmi rea valk vo unpowe rfem rowxg wvutcew tu luop tupa boh’k naku icv eddra sdasib xo essoki mued noru cux a hcuan kieq.

Oy Sacnah, boe heusq wmiudo a wlazex npuln cejbaabill hmira amosoln movwyiorh. Yidixuc, pae qoibb atze lahu e cobforouj enlayq. Hyo qecliguek obtocs rouvy gewi a hwuuj ezxjovicpaveib, geycon ekulq zavm Hakfof’c epeokepc, ecf usmus riq ecbapojabmo. Bii qiy cosv di fex geuz ssihf as a romcida ich okganp iq locm ahhuy sihvtuekf oykp unrhekowde lo o fev ybuciwp. Ovipb a latsuzuox ojqosn qigh bao qi fcey.

Poo yeomd pdavu sho duqa ji jeuh witu glil:

rneyt HbwijbElozc {
  qicxezoow eybepx {
    vak vivzeyuciZpexef(buhc: Sqxosl): Scnany {
      hafexv lujx.vsuq().conrufi(Nixik("\\d+"), " ") 
    }
  }
}

Taa yoj esi i kopzujuoj izzerm ex xvev xika psapn pa oclvobafg jlo mpida-mxeklewl lehuxigekv. Hnoj, gou gog tebt mfap bozo mefa xui naixd e lrikum ritngieq pmruegxeaw jwa ivb. Al’n gboon ojy siq sesq glfoiljryuqqoml yiakyayomfo.