Arrays

Arrays

배열을 다루기 편리한 메서드(static) 제공

 

1. 배열의 출력 - toString()

static String toString(boolean[] a)
static String toString(byte[] a)
static String toString(char[] a)
static String toString(short[] a)
static String toString(int[] a)
static String toString(long[] a)
static String toString(float[] a)
static String toString(double[] a)
static String toString(Object[] a)

 

2. 배열의 복사 - copyOf(), copyRange()

int[] arr = {0,1,2,3,4};
int[] arr2 = Arrays.copyOf(arr, arr.length); // arr2=[0,1,2,3,4]
int[] arr3 = Arrays.copyOf(arr, 3); // arr3=[0,1,2]
int[] arr4 = Arrays.copyOf(arr, 7); // arr4=[0,1,2,3,4,0,0]
int[] arr5 = Arrays.copyOfRange(arr, 2, 4); // arr5=[2,3] <- 4는 불포함
int[] arr6 = Arrays.copyOfRange(arr, 0, 7); // arr6=[0,1,2,3,4,0.0]

 

3. 배열 채우기- fill(), setAll()

int[] arr = new int[5];
Arrays.fill(arr, 9); // arr=[9,9,9,9,9]
Arrays.setAll(arr, (i) -> (int)(Math.random()*5)+1); // arr=[1,5,2,1,1]

 

4. 배열의 정렬과 검색 - sort(), binarySearch()

int[] arr = {3, 2, 0, 1, 4};
int idx = Arrays.binarySearch(arr, 2); // idx=-5 <- 잘못된 결과, 아직 배열이 정렬되어 있지 않기 때문

Arrays.sort(arr); // 배열 arr을 정렬
System.out.println(Arrays.toString(arr)); // [0, 1, 2, 3, 4]
int idx = Arrays.binarySearch(arr, 2); // idx = 2 <- 올바른 결과

 

5. 다차원 배열의 출력 - deepToString()

int[] arr = {0,1,2,3,4}; // 1차원
int[][] arr2D = {{11,12}, {21,22}}; // 2차원

System.out.println(Arrays.toString(arr)); // [0, 1, 2, 3, 4]
System.out.println(Arrays.deepToString(arr2D)); // [[11, 12], [21, 22]]

 

6. 다차원 배열의 비교 - deepEquals()

String[][] str2D = new String[][]{{"aaa", "bbb"}, {"AAA", "BBB"}};
String[][] str2D2 = new String[][]{{"aaa", "bbb"}, {"AAA", "BBB"}};

System.out.println(Arrays.equals(str2D, str2D2)); // false
System.out.println(Arrays.deepEquals(str2D, str2D2));// true

 

7. 배열을 List로 변환 - asList(Object...a)

List list = Arrays.asList(new Integer[]{1,2,3,4,5}); // list = [1, 2, 3, 4, 5]
List list = Arrays.asList(1,2,3,4,5); // list = [1, 2, 3, 4, 5]
list.add(6) // UnsupportedOperationException 예외 발생

List list = new ArraysList(Arrays.asList(1,2,3,4,5)); // 새로운 ArrayList

 

8. 람다와 스트림 관련 - parallelXXX(), spliterator(), stream()

 

 

코드

import java.util.Arrays;

public class ArraysTest {
    public static void main(String[] args) {
        int[] arr = {0,1,2,3,4};
        int[][]	arr2D = {{11,12,13}, {21,22,23}};

        System.out.println("arr="+ Arrays.toString(arr));
        System.out.println("arr="+ Arrays.toString(arr2D)); // 2차원 배열은 deepToString 사용하기, 이건 이상하게 나옴
        System.out.println("arr2D="+Arrays.deepToString(arr2D));
        System.out.println();

        int[] arr2 = Arrays.copyOf(arr, arr.length);
        int[] arr3 = Arrays.copyOf(arr, 3);
        int[] arr4 = Arrays.copyOf(arr, 7);
        int[] arr5 = Arrays.copyOfRange(arr, 2, 4);
        int[] arr6 = Arrays.copyOfRange(arr, 0, 7);

        System.out.println("arr2="+Arrays.toString(arr2));
        System.out.println("arr3="+Arrays.toString(arr3));
        System.out.println("arr4="+Arrays.toString(arr4));
        System.out.println("arr5="+Arrays.toString(arr5));
        System.out.println("arr6="+Arrays.toString(arr6));
        System.out.println();

        int[] arr7 =  new int[5];
        Arrays.fill(arr7, 9);  // arr=[9,9,9,9,9]
        System.out.println("arr7="+Arrays.toString(arr7));
        System.out.println();

        Arrays.setAll(arr7, i -> (int)(Math.random()*6)+1);
        System.out.println("arr7="+Arrays.toString(arr7));
        System.out.println();

        for(int i : arr7) { // 향상된 for문
            char[] graph = new char[i];
            Arrays.fill(graph, '*');
            System.out.println(new String(graph)+i);
        }
        System.out.println();

        String[][] str2D  = new String[][]{{"aaa","bbb"},{"AAA","BBB"}};
        String[][] str2D2 = new String[][]{{"aaa","bbb"},{"AAA","BBB"}};

        System.out.println(Arrays.equals(str2D, str2D2));     // false
        System.out.println(Arrays.deepEquals(str2D, str2D2)); // true
        System.out.println();

        char[] chArr = { 'A', 'D', 'C', 'B', 'E' };

        System.out.println("chArr="+Arrays.toString(chArr));
        System.out.println("index of B ="+Arrays.binarySearch(chArr, 'B')); // -2 잘못된 결과, 정렬을 안했기 때문
        System.out.println();

        Arrays.sort(chArr);
        System.out.println("chArr="+Arrays.toString(chArr));
        System.out.println("index of B ="+Arrays.binarySearch(chArr, 'B'));
    }
}


arr=[0, 1, 2, 3, 4]
arr=[[I@6aaa5eb0, [I@3498ed]
arr2D=[[11, 12, 13], [21, 22, 23]]

arr2=[0, 1, 2, 3, 4]
arr3=[0, 1, 2]
arr4=[0, 1, 2, 3, 4, 0, 0]
arr5=[2, 3]
arr6=[0, 1, 2, 3, 4, 0, 0]

arr7=[9, 9, 9, 9, 9]

arr7=[1, 6, 5, 5, 1]

*1
******6
*****5
*****5
*1

false
true

chArr=[A, D, C, B, E]
index of B =-2

chArr=[A, B, C, D, E]
index of B =1