鍘熷垱锛氭寜閽棩璁帮紙寰俊鍏紬鍙稩D锛歝odelogs锛夛紝娆㈣繋鍒嗕韩锛岃浆杞借淇濈暀鍑哄銆侷ntroductionjava8涔嬪悗锛屽湪甯哥敤鐨凪ap鎺ュ彛涓鍔犱簡涓€浜涢潪甯稿疄鐢ㄧ殑鍔熻兘锛屽彲浠ュぇ澶х畝鍖栦竴浜涚壒瀹氬満鏅殑浠ｇ爜缂栧啓锛屾彁楂樹唬鐮佺殑鍙鎬с€傝鎴戜滑鏉ョ湅鐪嬨€備互computeIfAbsent鍑芥暟涓轰緥锛屾垜浠粡甯搁渶瑕佸皢鏁版嵁鍒嗙粍鎴怣ap>鐨勫舰寮忋€傚湪java8涔嬪墠锛屼竴鑸槸杩欐牱瀹炵幇鐨勶細Listpayments=getPayments();Map>paymentByTypeMap=newHashMap<>();for(Paymentpayment:payments){if(!paymentByTypeMap.containsKey(payment.getPayTypeId())){paymentByTypeMap.put(payment.getPayTypeId(),newArrayList<>());}paymentByTypeMap.get(payment.getPayTypeId()).add(payment);}鍙互鍙戠幇鍙繘琛屼簡涓€娆″垎缁勬搷浣滐紝浣嗘槸浠ｇ爜闇€瑕佷粩缁嗚€冭檻銆傚綋Map涓病鏈夊搴旂殑鍊兼椂锛岄渶瑕佸厛鎻掑叆涓€涓┖鏍硷紝List杩涘幓銆備絾鏄鏋滀娇鐢╦ava8鎻愪緵鐨刢omputeIfAbsent鏂规硶锛屼唬鐮佷細绠€鍖栧緢澶氾紝濡備笅锛歀istpayments=getPayments();Map>paymentByTypeMap=newHashMap<>();for(Paymentpayment:payments){paymentByTypeMap.computeIfAbsent(payment.getPayTypeId(),k->newArrayList<>()).add(payment);}computeIfAbsent鏂规硶鐨勯€昏緫鏄鏋滄病鏈?Absent)map涓搴旂殑key锛岀劧鍚庢墽琛宭ambda琛ㄨ揪寮忕敓鎴愪竴涓粯璁ゅ€兼斁鍏ap涓繑鍥烇紝鍚﹀垯杩斿洖map涓凡鏈夌殑鍊笺€傚甫榛樿鍊肩殑Map鍥犱负杩欑闇€瑕侀粯璁ゅ€肩殑Map澶父瑙佷簡锛屾墍浠ユ垜涓€鑸皝瑁呬竴涓伐鍏风被浣跨敤锛屽涓嬶細publicclassDefaultHashMapextendsHashMap{Function鍔熻兘锛沺ublicDefaultHashMap(Suppliersupplier){this.function=k->supplier.get();}@Override@SuppressWarnings("unchecked")publicVget(Objectkey){returnsuper.computeIfAbsent((K)key,this.function);鐒跺悗鍍忚繖鏍蜂娇鐢ㄥ畠锛屽涓嬫墍绀猴細{paymentByTypeMap.get(payment.getPayTypeId()).add(payment);}鍛靛懙锛岃繖涓湁鐐瑰儚python鐨刣efaultdict(list)馃榿涓存椂缂撳瓨鏈夋椂鍊欙紝鍦╢or寰幆涓紝闇€瑕佷竴涓复鏃剁紦瀛樻潵澶嶇敤鏌ヨ缁撴灉寰幆锛屼篃鍙互浣跨敤computeIfAbcent锛屽涓嬫墍绀猴細heMap.computeIfAbsent(payment.getPayTypeId(),k->payTypeMapper.queryByPayType(k));payment.setPayTypeName(payType.getPayTypeName());}鍥犱负payments涓笉鍚宲ayment鐨刾ay_type_id寰堟湁鍙兘鏄竴鏍风殑锛屼娇鐢ㄨ繖涓柟娉曞彲浠ラ伩鍏嶅緢澶氶噸澶嶆煡璇紝浣嗘槸濡傛灉涓嶄娇鐢╟omputeIfAbcent鍑芥暟锛屼唬鐮佷細鏈夌偣楹荤儲鍜屾櫐娑┿€倂alue骞跺皢鍏舵斁鍏ap涓苟杩斿洖锛屽惁鍒欒繑鍥瀗ull銆傝繖涓嚱鏁颁竴鑸敤鍦ㄤ袱涓猻et鍏宠仈绛変环鐨勬椂鍊欙紝鍒ゆ柇閫昏緫鍙互灏戝啓涓€娆★紝濡備笅锛欯DatapublicstaticclassOrderPayment{privateOrderorder;绉佷汉娓呭崟<浠樻>浠樻锛沺ublicOrderPayment(璁㈠崟璁㈠崟){杩欎釜銆傝鍗?璁㈠崟锛泃his.payments=newArrayList<>();}publicOrderPaymentaddPayment(浠樻鏂瑰紡){this.payments.add(浠樻鏂瑰紡);褰掕繕杩欎釜锛泒}publicstaticvoidgetOrderWithPayment(){Listorders=getOrders();MaporderPaymentMap=newHashMap<>();for(Orderorder:orders){orderPaymentMap.put(order.getOrderId(),newOrderPayment(order));}Listpayments=getPayments();//灏嗘敮浠樹笌鐩稿叧璁㈠崟鐩稿叧鑱攠}computefunctioncompute鍑芥暟鍏跺疄鍜宑omputeIfPresent鍜宑omputeIfAbcent鍑芥暟绫讳技锛屽彧鏄笉鍏冲績mapvalue涓槸鍚︽湁鍊硷紝鎵цlambda琛ㄨ揪寮忚绠楀嚭鏂扮殑value鏀惧叆map涓繑鍥炪€傝鍑芥暟閫傜敤浜庡垎缁勮凯浠ｈ绠椼€傛瘮濡傛寜缁勬眹鎬婚噾棰濓紝灏遍€傚悎浣跨敤compute鍑芥暟锛屽涓嬶細Listpayments=getPayments();MapamountByTypeMap=newHashMap<>();for(Paymentpayment:payments){amountByTypeMap.compute(payment.getPayTypeId(),(key,oldVal)->oldVal==null?payment.getAmount():oldVal.add(payment.getAmount()));}褰搊ldValue涓簄ull锛岃〃绀哄湪map涓涓€娆¤绠楀搴攌ey鐨勫€硷紝鐩存帴缁欓噺灏卞ソ浜嗭紝鍚庨潰鍐嶆璁＄畻鐨勬椂鍊欙紝鐩存帴閫氳繃add鍑芥暟灏辨槸姝ｅソ銆俶erge鍑芥暟鍙互鍙戠幇涓婇潰浣跨敤compute姹囨€籥mount鏃讹紝lambda琛ㄨ揪寮忛渶瑕佸垽鏂槸鍚︽槸绗竴娆¤绠梜ey鍊硷紝鏈夌偣楹荤儲銆傚鏋滀娇鐢╩erge鍑芥暟锛岃繕鍙互杩涗竴姝ョ畝鍖栦唬鐮侊紝濡備笅锛歛mountByTypeMap.merge(payment.getPayTypeId(),payment.getAmount(),BigDecimal::add);}杩欎釜鍑芥暟澶畝娲佷簡馃槃锛宮erge绗竴涓弬鏁版槸key锛岀浜屼釜鍙傛暟鏄痸alue锛岀涓変釜鍙傛暟鏄€煎悎骞跺嚱鏁般€傜涓€娆¤绠楀搴攌ey鐨剉alue鏃讹紝鐩存帴灏唙alue鏀惧叆map涓€傚悗闈㈠啀娆¤绠楁椂锛屼娇鐢ㄥ€肩粍鍚堝嚱鏁癇igDecimal::add璁＄畻鍑轰竴涓柊鐨勬眹鎬诲€硷紝鏀惧叆map涓€俻utIfAbsent鍑芥暟putIfAbsent涔熷彲浠ヤ粠鍚嶅瓧灏辩煡閬撳畠鐨勪綔鐢ㄣ€傚綋map涓病鏈夊搴旂殑key鏃讹紝灏唙alue鏀惧叆map涓€備富瑕佺敤浜庝互涓嬪満鏅細姣斿灏唋ist杞崲涓簃ap鏃讹紝濡傛灉list涓瓨鍦ㄩ噸澶嶅€硷紝put鍜宲utIfAbsent鐨勫尯鍒涓嬶細put淇濈暀鏈€鏂版彃鍏ョ殑鏁版嵁銆俻utIfAbsent淇濈暀鏈€鏃х殑鎻掑叆鏁版嵁銆傝瀹炶瘽锛宩ava涓璮orEach鍑芥暟灏辨槸閬嶅巻map锛屽啓娉曟瘮杈冨暟鍡︼紝涓嶇鏄痚ntrySet鏂规硶杩樻槸keySet鏂规硶锛屽涓嬶細for(Map.Entryentry:amountByTypeMap.entrySet()){鏁存暟payTypeId=entry.getKey();BigDecimal閲戦=entry.getValue();System.out.printf("payTypeId:%s,amount:%s\n",payTypeId,amount);}鍐嶇湅python鎴栬€単o鍐欐硶濡備笅锛氬浜巔ayTypeId锛宎mount鍦╝mountByTypeMap.items()涓細print("payTypeId:%s,amount:%s\n"%(payTypeId,amount))鍙互鍙戠幇python涓殑map閬嶅巻鍐欐硶瑕佸皯鍐欏嚑琛屼唬鐮併€備笉杩囷紝铏界劧java鍦ㄨ娉曞眰闈笉鏀寔杩欑鍐欐硶锛屼絾鏄娇鐢╩ap鐨刦orEach鍑芥暟涔熷彲浠ョ畝鍖栫被浼肩殑鏁堟灉锛屽涓嬶細amountByTypeMap.forEach((payTypeId,amount)->{System.out.printf("payTypeId:%s,閲戦:%s\n",payTypeId,閲戦);});鎬荤粨Java涓€鐩磋寮€鍙戣€呰療鐥呭啓浠ｇ爜杩囦簬绻佺悙锛屼絾鏄粠java8寮€濮嬶紝浠嶮ap銆丼tream銆乿ar銆乵ultiline-string鍒皉ecord锛宩ava鍦ㄤ唬鐮佺紪鍐欏眰闈㈠仛浜嗗緢澶氱畝鍖栵紝鑰屼笖java濂藉儚寮€鎮熶簡馃
