Problem34 sunny

src/main/java/Practice/sunny/Chapter3/ArrayListPractice.java

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+package Practice.sunny.Chapter3;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Comparator;
+
+public class ArrayListPractice {
+
+  public static void main(String[] args) {
+
+    // Array
+    int[] odds = {1, 3, 5, 7, 9};
+    String[] weeks = {"월", "화", "수", "목", "금", "토", "일"};
+
+    // String[] weeks = new String[]; -> compile error
+    String[] weeks2 = new String[7];
+    weeks2[0] = "월";
+    weeks2[1] = "화";
+    weeks2[2] = "수";
+    weeks2[3] = "목";
+    weeks2[4] = "금";
+    weeks2[5] = "토";
+    weeks2[6] = "일";
+
+    // indexing
+    System.out.println(weeks[3]);
+
+    // length of array
+    for (int i = 0; i < weeks.length; i++) {
+      System.out.println(weeks[i]);
+    }
+
+    // ArrayIndexOutOfBoundsException
+    // System.out.println(weeks[7]);
+
+    // ArrayList
+    ArrayList pitches = new ArrayList();
+
+    // add
+    pitches.add("138");
+    pitches.add("129");
+    pitches.add("142");
+    pitches.add(0, "133");
+    pitches.add(2, "133");
+
+    // get
+    System.out.println(pitches.get(1));
+
+    // size
+    System.out.println(pitches.size());
+
+    // contains
+    System.out.println(pitches.contains("142"));
+
+    // remove
+    System.out.println(pitches.remove("129"));
+    System.out.println(pitches.remove(0));
+
+    // Generics
+    // ArrayList<String> pitches2 = new ArraList<String>();
+    ArrayList<String> pitches2 = new ArrayList<>();
+
+    ArrayList pitches3 = new ArrayList();
+    pitches3.add("138");
+    pitches3.add("129");
+    String one = (String) pitches3.get(0);
+    String two = (String) pitches3.get(1);
+
+    ArrayList<String> pitches4 = new ArrayList<>();
+    pitches4.add("138");
+    pitches4.add("129");
+    String three = pitches4.get(0);
+    String four = pitches4.get(1);
+
+    // asList
+    String[] data = {"138", "129", "142"};
+    ArrayList<String> pitches5 = new ArrayList<>(Arrays.asList(data));
+    System.out.println(pitches5);
+
+    ArrayList<String> pitches6 = new ArrayList<>(Arrays.asList("138", "129", "142"));
+    System.out.println(pitches6);
+
+    // String.join
+    String result = String.join(",", pitches6);
+    System.out.println(result);
+
+    String result2 = String.join(",", data);
+    System.out.println(result2);
+
+    // sort
+    pitches6.sort(Comparator.naturalOrder());
+    System.out.println(pitches6);
+  }
+}

src/main/java/Practice/sunny/Chapter3/CastingFinalPractice.java

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+package Practice.sunny.Chapter3;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+public class CastingFinalPractice {
+
+  public static void main(String[] args) {
+
+    // String to Integer
+    String num1 = "123";
+    int n1 = Integer.parseInt(num1);
+    System.out.println(n1);
+
+    // Integer to String
+    int n2 = 123;
+    String num2 = "" + n2;
+    System.out.println(num2);
+
+    int n3 = 123;
+    String num3 = String.valueOf(n3);
+    String num4 = Integer.toString(n3);
+    System.out.println(num3);
+    System.out.println(num4);
+
+    // String to Float
+    String num5 = "123.456";
+    double d = Double.parseDouble(num5);
+    System.out.println(d);
+
+    // Integer to Float
+    int n4 = 123;
+    double d1 = n4;
+    System.out.println(d1);
+
+    // Float to Integer
+    double d2 = 123.456;
+    int n5 = (int) d2;
+    System.out.println(n5);
+
+    // NumberFormatException Error
+    /*
+    String num = "123.456;
+    int n = Integer.parseInt(num);
+     */
+
+    // Final
+    final int n6 = 123;
+    // n6 = 456;  -> Compile Error
+
+    // Final List
+    final ArrayList<String> a = new ArrayList<>(Arrays.asList("a", "b"));
+    // a = new ArrayList<>(Arrays.asList("c", "d")); -> Compile Error
+
+    // List.of
+    final List<String> b = List.of("a", "b");
+    a.add("c");
+  }
+}

src/main/java/Practice/sunny/Chapter3/EnumPractice.java

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+package Practice.sunny.Chapter3;
+
+public class EnumPractice {
+
+  enum CoffeeType {
+    AMERICANO,
+    ICE_AMERICANO,
+    CAFE_LATE
+  }
+
+  ;
+
+  public static void main(String[] args) {
+
+    // print
+    System.out.println(CoffeeType.AMERICANO);
+    System.out.println(CoffeeType.ICE_AMERICANO);
+    System.out.println(CoffeeType.CAFE_LATE);
+
+    // for loop
+    for (CoffeeType type : CoffeeType.values()) {
+      System.out.println(type);
+    }
+
+    // Why use Enum
+    /*
+    int countSellCoffee(int type){
+      ...
+    }
+    int americano = countSellCoffee(1);
+    int result = countSellCoffee(99); -> error
+
+    int countSellCoffee(CoffeeType type){
+      ...
+     }
+     int americano = countSellCoffee(CoffeeType.AMERICANO);
+     */
+  }
+}

src/main/java/Practice/sunny/Chapter3/MapPractice.java

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+package Practice.sunny.Chapter3;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+
+public class MapPractice {
+
+  public static void main(String[] args) {
+
+    // HashMap
+    // put
+    HashMap<String, String> map = new HashMap<>();
+    map.put("people", "사람");
+    map.put("baseball", "야구");
+
+    // get
+    System.out.println(map.get("people"));
+    System.out.println(map.get("java"));
+    System.out.println(map.getOrDefault("java", "자바"));
+
+    // containsKey
+    System.out.println(map.containsKey("people"));
+
+    // remove
+    System.out.println(map.remove("people"));
+
+    // size
+    System.out.println(map.size());
+
+    // keySet
+    System.out.println(map.keySet());
+    List<String> keyList = new ArrayList<>(map.keySet());
+  }
+}

src/main/java/Practice/sunny/Chapter3/NumBoolPractice.java

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+package Practice.sunny.Chapter3;
+
+import java.nio.file.FileSystemNotFoundException;
+
+public class NumBoolPractice {
+
+  public static void main(String[] args) {
+
+    // Integer
+    int age = 10;
+    long countOfstar = 8764827384923849L;
+
+    // Float
+    float pi = 3.14F;
+    double morePi = 3.14159265358979323846;
+    double d1 = 123.4;
+    double d2 = 1.234e2;
+
+    // Oct, Hex
+    int octal = 023; // Decimal : 19
+    int hex = 0xC;   // Decimal : 12
+
+    // Add, Subtract, Multiply, Divide
+    int a = 10;
+    int b = 5;
+    System.out.println(a + b); // print 15
+    System.out.println(a - b); // print 5
+    System.out.println(a * b); // print 50
+    System.out.println(a / b); // print 2
+    System.out.println(7 % 3); // print 1
+    System.out.println(3 % 7); // print 3
+
+    // Increment, Decrement
+    int i = 1;
+    int j = 10;
+    i++;
+    j--;
+    System.out.println(i); // print 1
+    System.out.println(j); // print 9
+
+    i = 0;
+    System.out.println(i++); // print 0
+    System.out.println(i);   // print 1
+
+    i = 0;
+    System.out.println(++i); // print 1
+    System.out.println(i);   // print 1
+
+    // Boolean
+    boolean isSuccess = true;
+    boolean isTest = false;
+
+    // Boolean operation
+    // 2 > 1           -> true
+    // 1 == 2          -> false
+    // 3 % 2 == 1      -> true
+    // "3".equals("2") -> false
+
+    // Conditional
+    int base = 180;
+    int height = 185;
+    boolean isTall = height > base;
+
+    if (isTall) {
+      System.out.println("키가 큽니다."); // print 키가 큽니다.
+    }
+
+    i = 3;
+    boolean isOdd = i % 2 == 1;
+    System.out.println(isOdd);  // print true
+  }
+}

src/main/java/Practice/sunny/Chapter3/SetPractice.java

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+package Practice.sunny.Chapter3;
+
+import java.util.Arrays;
+import java.util.HashSet;
+
+public class SetPractice {
+
+  public static void main(String[] args) {
+
+    // HashSet
+    HashSet<String> set = new HashSet<>(Arrays.asList("H", "e", "l", "l", "o"));
+    System.out.println(set);
+
+    HashSet<Integer> s1 = new HashSet<>(Arrays.asList(1, 2, 3, 4, 5, 6));
+    HashSet<Integer> s2 = new HashSet<>(Arrays.asList(4, 5, 6, 7, 8, 9));
+
+    // Intersection
+    HashSet<Integer> intersection = new HashSet<>(s1);
+    intersection.retainAll(s2);
+    System.out.println(intersection);
+
+    // Union
+    HashSet<Integer> union = new HashSet<>(s1);
+    union.addAll(s2);
+    System.out.println(union);
+
+    // Relative Complement
+    HashSet<Integer> subtract = new HashSet<>(s1);
+    subtract.removeAll(s2);
+    System.out.println(subtract);
+
+    // Add
+    HashSet<String> set2 = new HashSet<>();
+    set2.add("Jump");
+    set2.add("to");
+    set2.add("Java");
+    System.out.println(set2);
+
+    // AddAll
+    HashSet<String> set3 = new HashSet<>();
+    set3.add("Jump");
+    set3.addAll(Arrays.asList("To", "Java"));
+    System.out.println(set3);
+
+    // Remove
+    HashSet<String> set4 = new HashSet<>();
+    set4.remove("To");
+    System.out.println(set4);
+
+  }
+}