4.1 Java Hello World
4.1.1 HelloWorld.java
ÀÚ¹ÙÀÇ Hello World¸¦ Ãâ·ÂÇÒ ½Ã°£ÀÔ´Ï´Ù. ¿©·¯ºÐµéÀÌ Hello World¸¦ Ãâ·ÂÇÏ´Â ¼ø°£ ´À³¥ ¼ö ÀÖ´Â °ÍÀº ¾Æ µÇ´Â±¸³ª¶ó´Â ´À³¦ÀÌ ÀÖÀ» °ÍÀÔ´Ï´Ù. ÇÏÁö¸¸ ¸ðµç °ÍÀÌ ¸ðÈ£ÇÕ´Ï´Ù. Â÷¶ó¸® ±× ¸ðµç °ÍÀ» ÀÚ¼¼È÷ ¾Ë¾Æ º¸µµ·Ï ÇϰڽÀ´Ï´Ù.
HelloWorld.java ¼Ò½ººÎÅÍ Çѹø º¸µµ·Ï ÇÏÁÒ.
HelloWorld.java(ÀÚ¹ÙÀÇ ±âº» ÇÁ·Î±×·¥ Å×½ºÆ®¸¦ À§ÇÑ ¿¹Á¦) |
public class HelloWorld{ public static void main(String[] args){ System.out.println("Hello World!"); } } |
Hello WorldÇÁ·Î±×·¥À» ÀÛ¼ºÇÏ¸é¼ ³ªÅ¸³ª´Â ÀÚ¹ÙÀÇ °³³äµéÀº ¾Æ·¡¿Í °°½À´Ï´Ù.
n main ¸Þ¼µå
n String¹è¿ String[]
n main ¸Þ¼µåÀÇ ¸Å°³º¯¼ö args
n staticŰ¿öµå
n System.out.println
n ¡°Hello World!¡± String
ÀÌ Ã¥Àº ÀüüÀûÀ¸·Î °£´ÜÇÏ°Ô ¼³¸íµÇ´Â °ÍµéÀ» ±æ°Ô ¼³¸íÇϰí ÀÖ½À´Ï´Ù. À̰ÍÀº ´ÜÁ¡ ¾Æ´Ñ ÀåÁ¡ÀÌ µÇ±æ ¹Ù¶ó¸é¼! ¾Ë°í °è½Ã´Ù¸é ÀÌ ÀýÀ» °Ç³Ê ¶ç¾îµµ ÁÁ½À´Ï´Ù.
4.1.2 main¸Þ¼µå
¸ðµç ÇÁ·Î±×·¥¿¡¼ main¸Þ¼µå´Â ÀÖ½À´Ï´Ù. ÀÚ¹ÙÀÇ main¸Þ¼µå´Â ¾Æ·¡¿Í °°Àº Çü½ÄÀ¸·Î µÇ¾î ÀÖ½À´Ï´Ù.
ÀÚ¹ÙÀÇ main¸Þ¼µå |
public static void main(String[] args) { } |
MainTest.java(ÀÚ¹ÙÀÇ main¸Þ¼µå) |
public class MainTest{ public void sayHello(){ System.out.println("Hello World!"); } public static void main(String[] args){ MainTest m = new MainTest(); m.sayHello(); } } |
C:\examples\4. Class for Basic Java>javac MainTest.java C:\examples\4. Class for Basic Java>java MainTest Hello World! |
4.1.3 String[] args
MainParam.java(ÀÚ¹ÙÀÇ main¸Þ¼µåÀÇ ¸Å°³º¯¼ö¸¦ Å×½ºÆ® Çϱâ À§ÇÑ ¿¹Á¦) |
public class MainParam { public static void main(String[] args){ System.out.println(args[0]); System.out.println(args[1]); } } |
C:\examples\4. Class for Basic Java>javac MainParam.java C:\examples\4. Class for Basic Java>java MainParam ¾È³ç! ÀÚ¹Ù ¾È³ç! ÀÚ¹Ù |
4.1.4 static
¿¹¸¦ µç´Ù¸é ¿©·¯ºÐÀÇ Çб³¿¡ ÄÄÇ»Åͽǿ¡ °£´Ù¸é ¸ðµç ÄÄÇ»ÅÍ´Â ÇϳªÀÇ ÆÐŰÁöó·³ ¸ðµç ¿ä¼Ò¸¦ Çϳª¾¿ ÀüºÎ °¡Áö°í ÀÖ½À´Ï´Ù. ±×¸®°í ÄÄÇ»ÅÍ ³»¿¡ ÇÁ¸°Æ®±îÁö ´Þ·Á ÀÖ½À´Ï´Ù. ÇÏÁö¸¸ ÇÁ¸°Æ®´Â ÇϳªÁÒ. ¸ðµç ÄÄÇ»ÅÍ¿¡¼ ÇÁ¸°Æ®´Â »ç¿ëÇÒ ¼ö ÀÖÁö¸¸ ÇÁ¸°Æ® Çϳª´Â ´Ù¸¥ °÷¿¡¼ °øÀ¯¸¦ ÇÏ´Â Çü½ÄÀ» »ç¿ëÇÕ´Ï´Ù. ÀÌ ¶§ ÇÁ¸°Æ®´Â staticÀ¸·Î ÀâÇô ÀÖ´Â °ÍÀÔ´Ï´Ù. °´Ã¼°¡ ¾Æ¹«¸® ¸¹ÀÌ »ý¼ºµÇ´õ¶óµµ ½ºÅÂÆ½ ¸â¹öÇʵå·Î ¼±¾ðµÇ¾î ÀÖÀ¸¸é ÇÁ·Î±×·¥ ³»¿¡¼ À¯ÀÏ ¹«ÀÏÇÑ ¸Þ¸ð¸®¸¦ Â÷ÁöÇÏ°Ô µË´Ï´Ù. ¸ðµç °´Ã¼¿¡¼ °øÅëÀ¸·Î »ç¿ëÇÏ´Â Àü¿ªº¯¼öÀÇ °³³äÀ¸·Î »ç¿ëÇÒ ¶§ ÀÌ staticÀ» »ç¿ëÇÕ´Ï´Ù. static¿¡ °üÇÑ °£´ÜÇÑ ¿¹¸¦ Çϳª »ìÆì º¸µµ·Ï ÇϰڽÀ´Ï´Ù.
StaticTest.java(½ºÅÂÆ½ ¸â¹öÇʵ带 Å×½ºÆ®Çϱâ À§ÇÑ ¿¹Á¦) |
public class StaticTest{ private static int sint=0; private int nint = 0; public StaticTest(){ sint = sint +1; nint = nint +1; } public void sayMember(){ System.out.println("sint:" + sint + " nint:" + nint); } public static void main(String[] args){ for(int i=0; i<10; i++){ StaticTest s = new StaticTest(); s.sayMember(); } } } |
C:\examples\4. Class for Basic Java>javac StaticTest.java C:\examples\4. Class for Basic Java>java StaticTest sint:1 nint:1 sint:2 nint:1 sint:3 nint:1 sint:4 nint:1 sint:5 nint:1 sint:6 nint:1 sint:7 nint:1 sint:8 nint:1 sint:9 nint:1 sint:10 nint:1 |
StaticTime.java(½ºÅÂÆ½ ¸â¹öÇʵåÀÇ Ãʱâȸ¦ Å×½ºÆ®Çϱâ À§ÇÑ ¿¹Á¦) |
public class StaticTime{ private static int sint=0; static{ sint = 100; System.out.println("sint:" + sint); } private int nint = 0; public static void main(String[] args){ StaticTime s = null; } } |
C:\examples\4. Class for Basic Java>javac StaticTime.java C:\examples\4. Class for Basic Java>java StaticTime sint:100 |
StaticAccess.java(½ºÅÂÆ½ ¸â¹öÇʵ忡 ´ëÇÑ Á¢±ÙÀ» Å×½ºÆ®Çϱâ À§ÇÑ ¿¹Á¦) |
public class StaticAccess{ public static int sint=0; public int nint =0; public static void main(String[] args){ StaticAccess.sint = 3333; System.out.println("½ºÅÂÆ½Á÷Á¢Á¢±Ù:" + StaticAccess.sint); } } |
C:\examples\4. Class for Basic Java>javac StaticAccess.java C:\examples\4. Class for Basic Java>java StaticAccess ½ºÅÂÆ½Á÷Á¢Á¢±Ù:3333 |
StaticAccessMethod.java(½ºÅÂÆ½ ¸â¹ö¸Þ¼µå¿¡ ´ëÇÑ Á¢±ÙÀ» Å×½ºÆ®Çϱâ À§ÇÑ ¿¹Á¦) |
public class StaticMethodAccess{ private static int sint=100; public int nint =0; public static void setStaticInt(int x){ sint = x; } public static int getStaticInt(){ return sint; } public static void main(String[] args){ StaticMethodAccess.setStaticInt(33333); int s = StaticMethodAccess.getStaticInt(); System.out.println("½ºÅÂÆ½°ªÀº:" + s); } } |
C:\examples\4. Class for Basic Java>javac StaticMethodAccess.java C:\examples\4. Class for Basic Java>java StaticMethodAccess ½ºÅÂÆ½°ªÀº:33333 |
4.1.5 System.out.println
4.1.6 °á·Ð
¿©·¯ºÐÀº ÀÌÁ¦ ºñ·Î¼Ò Hello World¶ó´Â ÀÚ¹Ù ÄÜ¼Ö Ãâ·Â ÇÁ·Î±×·¥À» ½ÃÀÛÇϽŠ°Ì´Ï´Ù. static¶§¹®¿¡ ¾à°£ ±î´Ù·Ó±â´Â ÇÏÁö¸¸ ´ëÃæÀÌ¶óµµ Hello WorldÀÇ ½É¿ÀÇÑ ¶æÀ» ÆÄ¾ÇÇÑ´Ù¸é ´ÙÀ½ °³³äÀ¸·Î Á¢±ÙÇϱ⠽¬¿öÁú °ÍÀÔ´Ï´Ù.
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