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Java System , String ๋ณธ๋ฌธ

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Java System , String

๊ธฐ๋Œ 2023. 11. 14. 18:44

๐Ÿ“š ๊ตญ๋น„ 22 ์ผ์ฐจ


 

๐Ÿ”ธ System ํด๋ž˜์Šค

  • Java ์‹คํ–‰ํ™˜๊ฒฝ์ด ์„ค์น˜๋œ ์‹œ์Šคํ…œ(์ปดํ“จํ„ฐ)์— ๋Œ€ํ•œ ๊ฐ’๊ณผ ๊ฐ์ฒด๋ฅผ ์ œ๊ณตํ•˜๋Š” ํด๋ž˜์Šค
  • java.lang ํŒจํ‚ค์ง€์— ์†ํ•ด์žˆ๋‹ค
  • Systemํด๋ž˜์Šค์˜ ๋ชจ๋“  ํ•„๋“œ์™€ ๋ชจ๋“  ๋ฉ”์„œ๋“œ๋Š” ์ •์  ํ•„๋“œ , ์ •์  ๋ฉ”์„œ๋“œ๋‹ค 
  • ์ œ๊ณต ํ•˜๋Š” ๊ฒƒ
    ํ‘œ์ค€ ์ž…๋ ฅ์žฅ์น˜ , ์ถœ๋ ฅ์žฅ์น˜ , ์—๋Ÿฌ์ถœ๋ ฅ์žฅ์น˜์™€ ์—ฐ๊ฒฐ๋œ ์ŠคํŠธ๋ฆผ
    ์ปดํ“จํ„ฐ ํ™˜๊ฒฝ๋ณ€์ˆ˜ , ํ”„๋กœํผํ‹ฐ ๊ฐ’
    ์ปดํ“จํ„ฐ ํ˜„์žฌ์‹œ๊ฐ„ ์ •๋ณด ์ œ๊ณต
package lang;

import java.util.Properties;

public class SystemApp1 {

	public static void main(String[] args) {
		
		/*
		 * long currentTimeMillis()
		 * ์œ ๋‹‰์Šค ํƒ€์ž„์€ 1970๋…„1์›”1์ผ0์‹œ0๋ถ„0์ดˆ๋ถ€ํ„ฐ ํ˜„์žฌ๊นŒ์ง€์˜ ์‹œ๊ฐ„์„
		 * 1 /1000 ๋‹จ์œ„๋กœ ํ‘œํ˜„ํ•œ ๊ฒƒ
		 */
		long unixTime = System.currentTimeMillis();
		
		System.out.println("์œ ๋‹‰์Šคํƒ€์ž„ : "+ unixTime);
		
		Properties props = System.getProperties();
		System.out.println(props);
		
		/*
		 * String getProperty(String name)
		 * 
		 */
		String value1 = System.getProperty("user.language");
		String value2 = System.getProperty("user.country");
		String value3 = System.getProperty("user.name");
		String value4 = System.getProperty("user.home");	
		String value5 = System.getProperty("user.dir");
		
		System.out.println("์–ธ์–ด : " + value1);				
		System.out.println("๊ตญ๊ฐ€ : " + value2); 			
		System.out.println("์‚ฌ์šฉ์ž ์ด๋ฆ„: " + value3); 		
		System.out.println("ํ™ˆ ๋””๋ ‰ํ† ๋ฆฌ ๊ฒฝ๋Ÿฌ : " + value4);
		System.out.println("ํ˜„์žฌ ๋””๋ ‰ํ† ๋ฆฌ : " + value5); 
//		์–ธ์–ด : ko
//		๊ตญ๊ฐ€ : KR
//		์‚ฌ์šฉ์ž ์ด๋ฆ„: Han
//		ํ™ˆ ๋””๋ ‰ํ† ๋ฆฌ ๊ฒฝ๋Ÿฌ : C:\Users\Han
//		ํ˜„์žฌ ๋””๋ ‰ํ† ๋ฆฌ : C:\workspace\Java-workspace\api
		
		/*
		 *  System.getenv(String name)
		 *  ์ง€์ •๋œ ์ด๋ฆ„์— ํ•ด๋‹นํ•˜๋Š” ํ™˜๊ฒฝ ๋ณ€์ˆ˜ ๊ฐ’ ๋ฐ˜ํ™˜
		 */
			
		String env1 = System.getenv("JAVA_HOME");
		String env2 = System.getenv("PATH");
		String env3 = System.getenv("TEMP");
		
		System.out.println("์ž๋ฐ” ํ™ˆ ๋””๋ ‰ํ† ๋ฆฌ : "+env1); 	
        // ์ž๋ฐ” ํ™ˆ ๋””๋ ‰ํ† ๋ฆฌ : C:\Program Files\Java\jdk-17
		System.out.println("path ์„ค์ •๋œ ๊ฒฝ๋กœ  : "+env2);
		System.out.println("์ž„์‹œ ๋””๋ ‰ํ† ๋ฆฌ ๊ฒฝ๋กœ : "+env3); 	
        // ์ž„์‹œ ๋””๋ ‰ํ† ๋ฆฌ ๊ฒฝ๋กœ : C:\Users\Han\AppData\Local\Temp
		


		
	}
}

 


๐Ÿ”ธ String

  • ๋ฌธ์ž์—ด์„ ํ‘œํ˜„ํ•˜๋Š” ๊ฐ์ฒด
  • ๋ฌธ์ž์—ด String์€ ๋ถˆ๋ณ€ ๊ฐ์ฒด๋‹ค โ–ถ ํ•œ๋ฒˆ ์ƒ์„ฑ๋œ ๋ฌธ์ž์—ด์€ ์ ˆ๋Œ€๋กœ ๋ณ€ํ•˜์ง€ ์•Š๋Š”๋‹ค
  • String ๊ฐ์ฒด์ƒ์„ฑ
String s = "abc";
  String s = new String("abc");
  
  char[] data = {'a', 'b', 'c'};
  String s = new String(data);

String๊ฐ์ฒด๋Š” ๋ฌธ์ž์—ด๊ณผ ๊ด€๋ จ๋œ ๋‹ค์–‘ํ•œ ๊ธฐ๋Šฅ์„ ์ œ๊ณตํ•œ๋‹ค

 

๐Ÿ”น String ์ฃผ์š” ๋ฉ”์„œ๋“œ

- int length ( )

  • ๋ฌธ์ž์—ด์˜ ๊ธธ์ด๋ฅผ ๋ฐ˜ํ™˜
String s3 = "์•ˆ๋…•ํ•˜์„ธ์š”";
String s4 = "";
String s5 = "    ";
System.out.println("๊ธธ์ด1 : " + s3.length());	// 5
System.out.println("๊ธธ์ด1 : " + s4.length());	// 0

 

- boolean equals (Objecct str)

  • ๋Œ€ / ์†Œ๋ฌธ์ž ๊ตฌ๋ถ„ํ•œ๋‹ค
  • ์ง€์ •๋œ ๋ฌธ์ž์—ด๊ณผ ๋ฌธ์ž์—ด์˜ ๋‚ด์šฉ์„ ๋น„๊ตํ•ด์„œ ์ผ์น˜ํ•˜๋ฉด true ๋ฐ˜ํ™˜
  • ๋ฌธ์ž์—ด์˜ '๋‚ด์šฉ'์„ ๋น„๊ต
String str1 = "๊น€๋นต๋นต";
String str2 = "๊น€๋นต๋นต";

String str3 = new String("๊น€๋นต๋นต");
String str4 = new String("๊น€๋นต๋นต");

System.out.println("์ฃผ์†Œ๊ฐ’ ๋น„๊ต : " + (str1 == str2));	// true
System.out.println("์ฃผ์†Œ๊ฐ’ ๋น„๊ต : " + (str3 == str4));	// false
System.out.println("์ฃผ์†Œ๊ฐ’ ๋น„๊ต : " + (str1 == str3));	// false

System.out.println("๋ฌธ์ž์—ด ๋‚ด์šฉ๋น„๊ต : " + str1.equals(str2));	// true 
System.out.println("๋ฌธ์ž์—ด ๋‚ด์šฉ๋น„๊ต : " + str3.equals(str4));	// true
System.out.println("๋ฌธ์ž์—ด ๋‚ด์šฉ๋น„๊ต : " + str1.equals(str3));	// true

 

- boolean equalsIgnoreCase(String str)

  • ๋Œ€/์†Œ๋ฌธ์ž ๊ตฌ๋ถ„ํ•˜์ง€ ์•Š๊ณ  ๋น„๊ต 
  • ๋ฌธ์ž์—ด ๋‚ด์šฉ๋น„๊ต ๋™๋“ฑ์„ฑ ์—ฌ๋ถ€ ๋ฐ˜ํ™˜
String str5 = "Hello";
String str6 = "hello";

System.out.println("๋Œ€์†Œ๋ฌธ์ž ๋ฌด์‹œ : " + str5.equalsIgnoreCase(str6));	// true
 System.out.println("๋Œ€์†Œ๋ฌธ์ž ๊ตฌ๋ถ„ : " + str5.equals(str6));	// false

 

- boolean ieEmpty()

  • ๋ฌธ์ž์—ด ๊ธธ์ด๊ฐ€ 0์ธ๊ฒฝ์šฐ true๋ฐ˜ํ™˜
  • ๊ธธ์ด๊ฐ€ 0 ์ธ ๋ฌธ์ž์—ด
  • " "
  String str1 = "";
  String str2 = " ";
  String str3 = "abc";

  boolean result1 = str1.isEmpty();	// true
  boolean result2 = str2.isEmpty(); // false
  boolean result3 = str3.isEmpty(); // false


- boolean contains(CharSequence s)

  • ์ง€์ •๋œ ๋ฌธ์ž์—ด์ด ํฌํ•จ๋˜์–ด ์žˆ์œผ๋ฉด true๋ฐ˜ํ™˜
String str6 = "ERP ์ฝ”ํผ๋ ˆ์ด์…˜";

System.out.println("๋ฌธ์ž์—ด์„ ํฌํ•จํ•˜๋Š”๊ฐ€ : " + str6.contains("์ฝ”ํผ")); // true

 

- int indexOf(String str) 

  • ์ง€์ •๋œ ๋ฌธ์ž์—ด์ด ์ฒ˜์Œ์œผ๋กœ ๋“ฑ์žฅํ•˜๋Š” ์œ„์น˜๋ฐ˜ํ™˜
  • ์ฐพ์„์ˆ˜ ์—†์œผ๋ฉด -1 ๋ฐ˜ํ™˜
  String str = "My car is red car";
  int index = str.indexOf("car");	// 3


- int lastIndexOf(String str)

  • ์ง€์ •๋œ ๋ฌธ์ž์—ด์ด ๋งˆ์ง€๋ง‰์œผ๋กœ ๋“ฑ์žฅํ•˜๋Š” ์œ„์น˜๋ฐ˜ํ™˜
  String str = "My car is red car";
  int index = str.lastiIndexOf("car");	// 14

 

- String substring(int beginIndex)

  • ์ง€์ •๋œ ์‹œ์ž‘์œ„์น˜ ~ ๋์œ„์น˜ ๋ฒ”์œ„์— ํ•ด๋‹นํ•˜๋Š” ๋ฌธ์ž์—ด์„ ์ƒˆ๋กœ ๋งŒ๋“ค์–ด์„œ ๋ฐ˜ํ™˜
  • ์ธ๋ฑ์Šค๋Š” 0๋ถ€ํ„ฐ ์‹œ์ž‘
String str1 = "ERP ์ฝ”ํผ๋ ˆ์ด์…˜";

String str2 = str1.substring(2);	
String str3 = str1.substring(2, 6);	

System.out.println(str2);		// P ์ฝ”ํผ๋ ˆ์ด์…˜
System.out.println(str3);		// P ์ฝ”ํผ

String str4 = "000305 - 3333852";

String str5 = str4.substring(0, 2);
System.out.println("ํƒœ์–ด๋‚œํ•ด : " + str5 + " ๋…„์ƒ");	// ํƒœ์–ด๋‚œํ•ด : 00 ๋…„์ƒ

String str6 = str4.substring(2, 6);
System.out.println("์ƒ์ผ : " + str6);					// ์ƒ์ผ : 0305

 

- String replace(String searchStr, String replaceStr)

  •   searchStr์— ํ•ด๋‹นํ•˜๋Š” ๋ฌธ์ž์—ด์ด replaceStr๋กœ ๋Œ€์ฒด๋œ ์ƒˆ๋ฌธ์ž์—ด์„ ๋ฐ˜ํ™˜ํ•œ๋‹ค
String str4 = "The red House's color is red";
String str5 = str4.replace("red", "Gray");
System.out.println("์›๋ณธ ๋ฌธ์ž์—ด : " + str4);	// ์›๋ณธ ๋ฌธ์ž์—ด : The red House's color is red
System.out.println("์ƒˆ๋กœ์šด ๋ฌธ์ž์—ด : " + str5); // ์ƒˆ๋กœ์šด ๋ฌธ์ž์—ด : The Gray House's color is Gray

 

- String replaceAll(String regex , String replacement)

  • ๋ฌธ์ž์—ด์—์„œ ์ง€์ •๋œ ์ •๊ทœํ‘œํ˜„์‹ ํŒจํ„ด์— ํ•ด๋‹นํ•˜๋Š” ๋ถ€๋ถ„์„ replacement ์—์„œ ์ง€์ •ํ•œ ๋ฌธ์ž์—ด์„ ์ƒˆ ๋ฌธ์ž์—ด๋กœ ๋ฐ˜ํ™˜
String str6 = "Red house's color is red";
String str7 = str6.replace("red", "green");
String str8 = str6.replaceAll("/red/i", "green");
System.out.println("์ƒˆ๋กœ์šด ๋ฌธ์ž์—ด : " + str7);	// Red house's color is green
System.out.println("์ƒˆ๋กœ์šด ๋ฌธ์ž์—ด : " + str8);	// Red house's color is red

 

- String toLowerCase()

  • ๋ฌธ์ž์—ด์„ ์†Œ๋ฌธ์ž๋กœ ์ƒˆ๋กœ ๋งŒ๋“ค์–ด์„œ ๋ฐ˜ํ™˜
String str1 = "Hello Eclipse";
String str3 = str1.toLowerCase();

System.out.println("์›๋ณธ ๋ฌธ์ž์—ด : " + str1);		// ์›๋ณธ ๋ฌธ์ž์—ด : Hello Eclipse
System.out.println("์ƒˆ๋กœ์šด ๋ฌธ์ž์—ด : " + str3);	// ์ƒˆ๋กœ์šด ๋ฌธ์ž์—ด : hello eclipse

 

- String toUpperCase()

  • ๋ฌธ์ž์—ด์„ ๋Œ€๋ฌธ์ž๋กœ ์ƒˆ๋กœ๋งŒ๋“ค์–ด์„œ ๋ฐ˜ํ™˜
String str1 = "Hello Eclipse";
String str2 = str1.toUpperCase();	
System.out.println("์›๋ณธ ๋ฌธ์ž์—ด : " + str1);		// ์›๋ณธ ๋ฌธ์ž์—ด : Hello Eclipse
System.out.println("์ƒˆ๋กœ์šด ๋ฌธ์ž์—ด : " + str2);	// ์ƒˆ๋กœ์šด ๋ฌธ์ž์—ด : HELLO ECLIPSE

 

- String trim()

  • ๋ฌธ์ž์—ด์„ ์ขŒ์šฐ ๋ถˆํ•„์š”ํ•œ ๊ณต๋ฐฑ์ด ์ œ๊ฑฐ๋œ ์ƒˆ๋กœ์šด ๋ฌธ์ž์—ด์„ ๋งŒ๋“ค์–ด์„œ ๋ฐ˜ํ™˜
/*
* String strip()
* 	` ๋ฌธ์ž์—ด์—์„œ ๋ถˆํ•„์š”ํ•œ ์ขŒ์šฐ ๊ณต๋ฐฑ์ด ์ œ๊ฑฐ๋œ ์ƒˆ๋ฌธ์ž์—ด์„ ๋ฐ˜ํ™˜
*
* String stripLeading()
* 	` ๋ฌธ์ž์—ด์—์„œ ์™ผ์ชฝ ๊ณต๋ฐฑ์ด ์ œ๊ฑฐ๋œ ์ƒˆ ๋ฌธ์ž์—ด ๋ฐ˜ํ™˜
*
* String stripTrailing()
* 	` ๋ฌธ์ž์—ด์—์„œ ์˜ค๋ฅธ์ชฝ ๊ณต๋ฐฑ์ด ์ œ๊ฑฐ๋œ ์ƒˆ ๋ฌธ์ž์—ด ๋ฐ˜ํ™˜
*/

String str9 = "    ๋ฐ˜๊ฐ‘ ์Šต๋‹ˆ๋‹ค      ์ž…๋‹ˆ๋‹ค      ";
String str10 = str9.trim();
String str11 = str9.strip();
String str12 = str9.stripLeading();
String str13 = str9.stripTrailing();

System.out.println("์›๋ณธ ๋ฌธ์ž์—ด : [" + str9 + "]");	// ์›๋ณธ ๋ฌธ์ž์—ด : [    ๋ฐ˜๊ฐ‘ ์Šต๋‹ˆ๋‹ค      ์ž…๋‹ˆ๋‹ค      ]
System.out.println("์ƒˆ๋กœ์šด ๋ฌธ์ž์—ด1 : [" + str10 + "]");	// ์ƒˆ๋กœ์šด ๋ฌธ์ž์—ด1 : [๋ฐ˜๊ฐ‘ ์Šต๋‹ˆ๋‹ค      ์ž…๋‹ˆ๋‹ค]
System.out.println("์ƒˆ๋กœ์šด ๋ฌธ์ž์—ด2 : [" + str11 + "]");	// ์ƒˆ๋กœ์šด ๋ฌธ์ž์—ด2 : [๋ฐ˜๊ฐ‘ ์Šต๋‹ˆ๋‹ค      ์ž…๋‹ˆ๋‹ค]
System.out.println("์ƒˆ๋กœ์šด ๋ฌธ์ž์—ด3 ์™ผ์ชฝ ๊ณต๋ฐฑ์ œ๊ฑฐ: [" + str12 + "]");	// ์ƒˆ๋กœ์šด ๋ฌธ์ž์—ด3 ์™ผ์ชฝ ๊ณต๋ฐฑ์ œ๊ฑฐ: [๋ฐ˜๊ฐ‘ ์Šต๋‹ˆ๋‹ค      ์ž…๋‹ˆ๋‹ค      ]
System.out.println("์ƒˆ๋กœ์šด ๋ฌธ์ž์—ด4 ์˜ค๋ฅธ์ชฝ ๊ณต๋ฐฑ์ œ๊ฑฐ: [" + str13 + "]");	// ์ƒˆ๋กœ์šด ๋ฌธ์ž์—ด4 ์˜ค๋ฅธ์ชฝ ๊ณต๋ฐฑ์ œ๊ฑฐ: [    ๋ฐ˜๊ฐ‘ ์Šต๋‹ˆ๋‹ค      ์ž…๋‹ˆ๋‹ค]

 

- boolean startsWith(String Prefix)

  • ๋ฌธ์ž์—ด์ด ์ง€์ •๋œ prefix๋ฅผ ์‹œ์ž‘ํ•˜๊ณ  ์žˆ๋‹ค๋ฉด true ๋ฐ˜ํ™˜
String str7 = "http://projectSyuSyu/syusyu/notice";
String str8 = "https://localhost/8080/intdex.html";
String str9 = "https://kmooc.udemy.com/organization/home/";

System.out.println("๋ฌธ์ž์—ด์ด https ์‹œ์ž‘ ํ•˜๋Š”๊ฐ€ :" + str7.startsWith("https"));	// false
System.out.println("๋ฌธ์ž์—ด์ด https ์‹œ์ž‘ ํ•˜๋Š”๊ฐ€ :" + str8.startsWith("https"));	// true
System.out.println("๋ฌธ์ž์—ด์ด http ์‹œ์ž‘ ํ•˜๋Š”๊ฐ€ :" + str9.startsWith("http"));	// false

 

- boolean endsWith(String suffix)

  • ๋ฌธ์ž์—ด์ด ์ง€์ •๋œ suffix๋กœ ๋๋‚˜๋ฉด true ๋ฐ˜ํ™˜
String str10 = "sample.hwp";
String str11 = "sample2.xlsx";
String str12 = "sample.xml";

System.out.println("์—‘์…€ ํŒŒ์ผ์ธ๊ฐ€ ? : " + str10.endsWith("xlsx"));	// false
System.out.println("์—‘์…€ ํŒŒ์ผ์ธ๊ฐ€ ? : " + str11.endsWith("xlsx"));	// true
System.out.println("์—‘์…€ ํŒŒ์ผ์ธ๊ฐ€ ? : " + str12.endsWith("xlsx"));	// false

 

- String [] split(String regax)

  • ๋ฌธ์ž์—ด์„ ์ง€์ •๋œ ๊ตฌ๋ถ„ ๋ฌธ์ž์—ด๋กœ ์ž˜๋ผ์„œ ๊ฐ๊ฐ์š”์†Œ๋ฅผ ๋ฐฐ์—ด์— ๋‹ด์•„ ๋ฐ˜ํ™˜
String str = "๊ณฝ์žฌ์šฐ,๊น€์œ ์‹ ,๊น€์‹œ๋ฏผ,์†๊ถŒ,ํƒœ์‚ฌ์ž";
String[] result = str.split(",");

// ์ถœ๋ ฅ 1๋ฒˆ๋ฐฉ๋ฒ•
System.out.println(result[0]);
System.out.println(result[1]);
System.out.println(result[2]);
System.out.println(result[3]);
System.out.println(result[4]);

// ์ถœ๋ ฅ 2๋ฒˆ๋ฐฉ๋ฒ•
System.out.println(Arrays.toString(result));	// [๊ณฝ์žฌ์šฐ, ๊น€์œ ์‹ , ๊น€์‹œ๋ฏผ, ์†๊ถŒ, ํƒœ์‚ฌ์ž]

// ์ถœ๋ ฅ 3๋ฒˆ ๋ฐฉ๋ฒ•
for (String value : result) {
System.out.println(value);
}

 

- int comapareTo(String other)

  • ์ง€์ •๋œ ๋‹ค๋ฅธ๋ฌธ์ž์™€ ์‚ฌ์ „์ˆœ์„œ๋Œ€๋กœ ๋น„๊ต
  • ๋ฐฐ์—ด์ด๋‚˜ ์ปฌ๋ ‰์…˜์— ์ €์žฅ๋œ ๋ฌธ์ž์—ด์„ ์ •๋ ฌํ•  ๋•Œ ์‚ฌ์šฉ
String a = "apple";
String b = "banana";

int result = a.compareTo(b);  // ๋ฐ˜ํ™˜ ๊ฐ’์œผ๋กœ -1 0 ์–‘์˜์ •์ˆ˜ ์ถœ๋ ฅ

System.out.println(result); // -1

 

- char charAt(int index)

  • ๋ฌธ์ž์—ด์—์„œ ์ง€์ •๋œ ์œ„์น˜์˜ ๊ธ€์ž ํ•˜๋‚˜๋ฅผ ๋ฌธ์ž๋กœ ๋ฐ˜ํ™˜
  String str = "abc";
  char c = str.charAt(0);	// 'a'

 

- static String valueOf(๋‹ค์–‘ํ•œ ๊ฐ’)

  • ์ „๋‹ฌ๋ฐ›์€ ๋‹ค์–‘ํ•œ ํƒ€์ž…์˜ ๊ฐ’์„ ๋ฌธ์ž์—ด๋กœ ๋ฐ”๊ฟ”์„œ ๋ฐ˜ํ™˜
  • ์ •์ ๋ฉ”์„œ๋“œ
  String result1 = String.valueOf(10);	// "10"
  String result2 = String.valueOf(3.14);	// "3.14"
  String result3 = String.valueOf(true);	// "true"

 

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