Java 변환

int[] to Integer[]

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        int[] a = {1,2,3,4};
        Integer[] b = Arrays.stream(a)
                .boxed()
                .toArray(Integer[]::new);
        System.out.println(Arrays.toString(b));
    }
}

Integer[] to int []

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        Integer[] a = {1,2,3,4};
        int[] b = Arrays.stream(a).mapToInt(Integer::intValue).toArray();
        System.out.println(Arrays.toString(b));
    }
}

int[] to string[]

import java.util.*;

public class Main {
    public static void main(String[] args) {
        int a = 123;
        String b = String.valueOf(a);
        System.out.println(b);  // 123

        int[] c = {1, 55, 129};
        String[] d = Arrays.stream(c).mapToObj(String::valueOf).toArray(String[]::new);
        System.out.println(Arrays.toString(d)); // [1, 55, 129]
    }
}

string[] to int[]

import java.util.*;

public class Main {
    public static void main(String[] args) {
        String[] a = {"1", "2", "3", "4"};
        int[] b = Arrays.stream(a).mapToInt(Integer::valueOf).toArray();
        System.out.println(Arrays.toString(b));
    }
}

int[] to List<Integer>

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        int[] arr = {1, 2, 3, 4, 5};
        List<Integer> list = Arrays.stream(arr)  // IntStream
                .boxed()  // Stream<Integer>
                .collect(Collectors.toList());
        System.out.println(list);
    }
}

List<Integer> to int[] 

import java.util.Arrays;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);
        int[] arr = list.stream().mapToInt(Integer::intValue).toArray();
        System.out.println(Arrays.toString(arr));
    }
}

char[] to String

public class Main {
    public static void main(String[] args) {
        var c = new char[]{'a', 'b', 'c'};
        var s1 = String.valueOf(c);
        System.out.println(s1);
        var s2 = String.copyValueOf(c);
        System.out.println(s2);
        // valueOf와 copyValueOf는 같다. 
    }
}

String to char[]

public class Main {
    public static void main(String[] args) {
        var s = "abcdefg";
        char[] c = s.toCharArray();
        System.out.println(c);
    }
}