Array

1. Print Array - toString()

//by overloading method
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. Copy Array - copyOf(), copyOfRange()

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], does not including 4
int[] arr6 = Arrays.copyOfRange(arr,0,7);//arr6 = [0,1,2,3,4,0,0]

3. Fill out Array - fill( ), setAll() - fill( ): Fill out with specific vaue(number,...) - setAll() : Fill out with Lambda.

int[] arr = new int[5];
Arrays.fill(arr,9);//arr=[9,9,9,9,9]
// 1 <= x < 6
//arr=[1,5,2,1,1]
Arrays.setAll(arr,(i) -> (int)(Math.random()*5)+1);

4. Sort and Serarch Array - sort(), binarySearch() - binarySearch() : Only when array is sorted. So, you should sort the array first.

int[] arr = {3,2,0,1,4};
int idx = Arrays.binarySearch(arr,2);//idx=-5 <- wrong result.

Arrays.sort(arr);
System.out.println(Arrays.toString(arr));//[0,1,2,3,4]
int idx = Arrays.binarySearch(arr,2);//idx=2 <-correct result.

5. Print Multiple-dimensional Array - deepToString( )

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

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

6. Compare Multiple-dimensional Array - 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. Casting Array to List - asList(Object ...a) - asList(Object...a) : Mutable parameter. The number of parameter is not defined. - List is for read data.

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

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

• 배열 출력

int[] iArr = {100,95,80,70,60};
System.out.println(iArr);//[I@14318bb] 같은 형식의 문자열 출력

char[] chArr = {'a','b','c','d'};
System.out.println(chArr);//abcd 출력

• 배열 출력 - Arrays.toString() 이용(많이 사용) : iArr의 배열 값들을 String으로 바꿔주고 이 String을 출력한다. 한번에 출력되기 때문에 편하다.

System.out.println(Arrays.toString(iArr));