4 java lang Math 15 4 java lang
- Slides: 29
4. java. lang 패키지 Math 클래스 15
4. java. lang 패키지 Math 클래스 16
4. java. lang 패키지 Math 클래스 예제 public class Math. Test { public static void main(String[] args){ double x = Math. PI; System. out. println(Math. sin(x)); System. out. println(Math. random()); } } 17 Math. Test. java
4. java. lang 패키지 Class 클래스 n 임의의 인스턴스에게 클래스 정보를 가져올 때 활용 Class 클래스 예제 Toy. Test. java import java. util. Date; interface Has. Batteries {} interface Waterproof {} interface Shoots. Things {} class Toy { Toy() {} Toy(int i) {} } class Fancy. Toy extends Toy implements Has. Batteries, Waterproof, Shoots. Things { Fancy. Toy() { super(1); } } 19
4. java. lang 패키지 Class 클래스 예제 (계속) Toy. Test. java public class Toy. Test { public static void main(String[] args) throws Exception { Class c = Class. for. Name("Fancy. Toy"); print. Info(c); Class[] faces = c. get. Interfaces(); for(int i = 0; i < faces. length; i++) print. Info(faces[i]); Class cy = c. get. Superclass(); print. Info(cy); Date d = new Date(); print. Info(d. get. Class()); } static void print. Info(Class cc) { System. out. println("Class name: " + cc. get. Name() + " is interface? [" + cc. is. Interface } } 20
4. java. lang 패키지 System 클래스 예제 public class System. Test { public static void main(String[] args) { System. out. println(System. current. Time. Millis()); System. out. println(System. nano. Time()); System. exit(0); } } 22 System. Test. java
4. java. lang 패키지 포장 (wrapper) 클래스 n Java 1. 5 부터 제공하는 Auto-boxing 및 Unboxing 기능 Integer box = new Integer(10); System. out. println(box + 1); // box는 자동으로 int형으로 변환 n 26
4. java. lang 패키지 포장 (wrapper) 클래스 n Auto-boxing 및 Unboxing 의 예 Integer int. Object = new Integer(10); int. Primitive = int. Object. int. Value(); int. Primitive++; int. Object = new Integer(int. Primitive); n Integer int. Object = new Integer(10); int. Object++; Auto-boxing 및 Unboxing 의 다른 예 Boolean is. Valid = false; // Boxing Short short. Object = 200; // Boxing if(short. Object < 20){ …} // unboxing Array. List<Integer> list = new Array. List<Integer>(); for(int i = 0; i < 10; i++){ list. add(i); // Boxing } 27
4. java. lang 패키지 String. Buffer 클래스 n 29 주요 메소드
4. java. lang 패키지 String. Buffer 클래스 예제 1 public class String. Speed. Test { public static void main(String[] args) { String abc 1 = ""; long start = System. nano. Time(); for (int i = 0; i < 10000; i++) { abc 1 += "abc"; } long end = System. nano. Time(); System. out. println("Test 1: " + (end - start)); //System. out. println(abc 1); 30 String. Speed. Test. java
4. java. lang 패키지 String. Buffer 클래스 예제 1 (계속) String. Buffer abc 2 = new String. Buffer(); start = System. nano. Time(); for (int i = 0; i < 10000; i++) { abc 2. append("abc"); } end = System. nano. Time(); System. out. println("Test 2: " + (end - start)); //System. out. println(abc 2); String. Buffer abc 3 = new String. Buffer(30000); start = System. nano. Time(); for (int i = 0; i < 10000; i++) { abc 3. append("abc"); } end = System. nano. Time(); System. out. println("Test 3: " + (end - start)); //System. out. println(abc 3); } 31} String. Speed. Test. java
4. java. lang 패키지 String. Buffer 클래스 예제 2 public class String. Buffer. Test { public static void main(String[] args) { String. Buffer sb = new String. Buffer("10+20="); sb. append(10+20); sb. insert(0, "수식 "); System. out. println(sb); } } 32 String. Buffer. Test. java
5. java. util 패키지 Random 클래스 예제 String. Buffer. Test. java import java. util. Random; public class Random. Test { public static void main(String[] args) { Random random = new Random(System. current. Time. Millis()); for (int i = 0; i < 10; i++) System. out. println(random. next. Int(100)); } } 34
5. java. util 패키지 Arrays 클래스 예제 String. Buffer. Test. java import java. util. Arrays; public class Arrays. Test { public static void main(String[] args) { int[] array = { 9, 4, 5, 6, 2, 1 }; Arrays. sort(array); print. Array(array); System. out. println(Arrays. binary. Search(array, 9)); Arrays. fill(array, 8); print. Array(array); } private static void print. Array(int[] array) { System. out. print("["); for (int i = 0; i < array. length; i++) System. out. print(array[i] + " "); System. out. println("]"); } } 36
5. java. util 패키지 Date 클래스 n n Millisecond 단위로 현재시각을 나타냄 Java 1. 2 이후부터 Calendar 클래스 사용이 장려됨 Calendar 클래스 n Calendar 객체 얻어오는 방법 w Calendar right. Now = Calendar. get. Instance(); 37
5. java. util 패키지 Calendar 클래스 예제 import java. util. *; public class Calendar. Test { public static void main(String[] args) { Calendar d = Calendar. get. Instance(); System. out. println(d. get(Calendar. YEAR) + "년"); System. out. println(d. get(Calendar. MONTH) + 1 + "월"); System. out. println(d. get(Calendar. DATE) + "일"); d. set(Calendar. HOUR, 12); d. set(Calendar. MINUTE, 34); d. set(Calendar. SECOND, 0); System. out. println(d); } } 38 String. Buffer. Test. java
5. java. util 패키지 String. Tokenizer 클래스 예제 String. Test. java import java. util. *; public class String. Test { public static void main(String[] args) { String. Tokenizer st = new String. Tokenizer("Will Java change my life? "); while (st. has. More. Tokens()) { System. out. println(st. next. Token()); } } } 40
5. java. util 패키지 String. Tokenizer 클래스 예제 String. Tokenizer. Sample. java import java. util. String. Tokenizer; public class String. Tokenizer. Sample { public static void main(String[] args) { String. Tokenizer st = new String. Tokenizer("a stringtokenizer sample"); System. out. println("tokens count: " + st. count. Tokens()); while (st. has. More. Elements()) { String token = st. next. Element(). to. String(); System. out. println("token = " + token); } st = new String. Tokenizer("2005/12/15 - 09: 17: 28", "/: - "); while (st. has. More. Elements()) { String token = st. next. Token(); System. out. println("token = " + token); } } 41}
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