Java Program\u0131n\u0131n \u00c7al\u0131\u015fma S\u0131ras\u0131: Ad\u0131m Ad\u0131m Anlat\u0131m<\/p>\n
Merhaba! Bug\u00fcn, Java programlama yolculu\u011fumuzun d\u00f6rd\u00fcnc\u00fc g\u00fcn\u00fcnde, bir Java program\u0131n\u0131n nas\u0131l \u00e7al\u0131\u015ft\u0131\u011f\u0131na, yani y\u00fcr\u00fctme ak\u0131\u015f\u0131na (execution flow) derinlemesine dalaca\u011f\u0131z. Bu, Java’da ba\u015far\u0131l\u0131 olmak i\u00e7in temel ve olduk\u00e7a \u00f6nemli bir konudur. \u00d6ncelikle, bir program\u0131n nas\u0131l yaz\u0131ld\u0131\u011f\u0131n\u0131 anlad\u0131\u011f\u0131m\u0131z\u0131 varsayarak ilerleyece\u011fiz. Daha \u00f6nceki yaz\u0131lar\u0131mda bu konulara de\u011findi\u011fimi hat\u0131rlatmak isterim. Bu yaz\u0131da, derleme ve \u00e7al\u0131\u015fma zaman\u0131 s\u00fcre\u00e7lerini, de\u011fi\u015fken kapsam\u0131n\u0131 ve kontrol ak\u0131\u015f\u0131n\u0131 ayr\u0131nt\u0131l\u0131 bir \u015fekilde inceleyece\u011fiz.<\/p>\n
Bir Java program\u0131n\u0131 \u00e7al\u0131\u015ft\u0131rmadan \u00f6nce, \u00f6ncelikle derlenmesi gerekir. Bu s\u00fcre\u00e7te, yazd\u0131\u011f\u0131m\u0131z insan taraf\u0131ndan okunabilir Java kodu, Java Virtual Machine (JVM) taraf\u0131ndan anla\u015f\u0131labilir bir ara dil olan bytecode’a d\u00f6n\u00fc\u015ft\u00fcr\u00fcl\u00fcr. Bu d\u00f6n\u00fc\u015f\u00fcm\u00fc, Java Derleyicisi (javac) ger\u00e7ekle\u015ftirir. Derleyici, yaz\u0131m hatalar\u0131n\u0131 (syntax errors) ve baz\u0131 t\u00fcr hatalar\u0131n\u0131 (type errors) tespit ederek size bildirir. Bu hatalar\u0131 d\u00fczeltmeden, program\u0131n\u0131z \u00e7al\u0131\u015fmaz. \u00d6rne\u011fin, a\u015fa\u011f\u0131daki gibi bir kod par\u00e7as\u0131, derleme zaman\u0131nda hata verecektir:<\/p>\n
\npublic class Main {\n public static void main(String[] args) {\n int x = 10;\n String y = x; \/\/ Type mismatch error\n }\n}\n<\/code><\/pre>\nYukar\u0131daki \u00f6rnekte, bir integer de\u011fi\u015fkenini String de\u011fi\u015fkenine do\u011frudan atayamay\u0131z. Bu, derleme zaman\u0131nda bir hata olu\u015fmas\u0131na neden olur. Bu nedenle, derleme a\u015famas\u0131, program\u0131m\u0131z\u0131n do\u011fru bir \u015fekilde yaz\u0131ld\u0131\u011f\u0131ndan emin olmak i\u00e7in son derece \u00f6nemlidir.<\/p>\n
\u00c7al\u0131\u015fma Zaman\u0131 (Runtime)<\/h2>\n
Derleme ba\u015far\u0131l\u0131 olduktan sonra, ortaya \u00e7\u0131kan bytecode dosyas\u0131 JVM taraf\u0131ndan yorumlan\u0131r ve \u00e7al\u0131\u015ft\u0131r\u0131l\u0131r. JVM, platform ba\u011f\u0131ms\u0131zl\u0131\u011f\u0131n\u0131 sa\u011flayan \u00f6nemli bir bile\u015fendir. Yani, bir i\u015fletim sisteminde derlenen Java kodu, farkl\u0131 bir i\u015fletim sisteminde JVM ile \u00e7al\u0131\u015ft\u0131r\u0131labilir. \u00c7al\u0131\u015fma zaman\u0131nda, bellekte veri yap\u0131lar\u0131n\u0131n olu\u015fturulmas\u0131, metotlar\u0131n \u00e7a\u011fr\u0131lmas\u0131 ve i\u015flemlerin y\u00fcr\u00fct\u00fclmesi gibi i\u015flemler ger\u00e7ekle\u015fir. Bu s\u00fcre\u00e7te, runtime exception’lar (\u00f6rne\u011fin, NullPointerException) olu\u015fabilir ve bunlar\u0131n do\u011fru bir \u015fekilde y\u00f6netilmesi gerekir.<\/p>\n
De\u011fi\u015fken Kapsam\u0131 (Variable Scope)<\/h2>\n
De\u011fi\u015fken kapsam\u0131, bir de\u011fi\u015fkenin program\u0131n hangi b\u00f6l\u00fcmlerinde eri\u015filebilir oldu\u011funu belirler. \u00d6rne\u011fin, bir metot i\u00e7inde tan\u0131mlanan bir de\u011fi\u015fken, sadece o metot i\u00e7inde eri\u015filebilirdir. Bu, kodun okunabilirli\u011fini ve bak\u0131m\u0131n\u0131 kolayla\u015ft\u0131r\u0131r. Ayr\u0131ca, kodunuzda olas\u0131 hatalar\u0131n olu\u015fmas\u0131n\u0131 \u00f6nlemek i\u00e7in de\u011fi\u015fken kapsam\u0131n\u0131 do\u011fru bir \u015fekilde y\u00f6netmek \u00f6nemlidir. Do\u011fru de\u011fi\u015fken kapsam\u0131 kullan\u0131m\u0131na dikkat edilmezse program \u00e7al\u0131\u015fmas\u0131 s\u0131ras\u0131nda beklenmedik sonu\u00e7lar al\u0131nabilir.<\/p>\n
Kontrol Ak\u0131\u015f\u0131 (Control Flow)<\/h2>\n
Kontrol ak\u0131\u015f\u0131, program\u0131n hangi komutlar\u0131n hangi s\u0131rayla y\u00fcr\u00fct\u00fclece\u011fini belirler. Ko\u015fullu ifadeler (if-else), d\u00f6ng\u00fcler (for, while) ve switch-case yap\u0131lar\u0131n\u0131 kullanarak program\u0131n ak\u0131\u015f\u0131n\u0131 kontrol edebilir ve farkl\u0131 senaryolara g\u00f6re farkl\u0131 i\u015flemler ger\u00e7ekle\u015ftirebiliriz. Bu, program\u0131n esnekli\u011fini ve i\u015flevselli\u011fini art\u0131r\u0131r. Karma\u015f\u0131k programlar yazarken do\u011fru kontrol ak\u0131\u015f\u0131 kullan\u0131m\u0131, kodu daha anla\u015f\u0131labilir ve hata ay\u0131klamas\u0131 daha kolay hale getirir.<\/p>\n
\u00d6rne\u011fin, bir ko\u015fullu ifade:<\/p>\n
\nif (x > 10) {\n System.out.println(\"x, 10'dan b\u00fcy\u00fck\");\n} else {\n System.out.println(\"x, 10'dan k\u00fc\u00e7\u00fck veya e\u015fit\");\n}\n<\/code><\/pre>\nProgram\u0131n ak\u0131\u015f\u0131n\u0131, x de\u011fi\u015fkeninin de\u011ferine ba\u011fl\u0131 olarak y\u00f6nlendirir. Bu yap\u0131, Java programlaman\u0131n temel ta\u015flar\u0131ndan biridir.<\/p>\n