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Ch.06 배열 Array

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배열 선언

데이터 타입[] 변수명; 데이터 타입 변수명[];

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int[] arrInt;
int arrInt2[];
 
double[] arrDouble;
String[] arrString;

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package chapter06;
 
public class ArrEx {
 
    public static void main(String[] args) {
         
        int[] arrInt;
        int arrInt2[];
         
        double[] arrDouble;
        String[] arrString;
         
 
    }
 
}
 
<code>
 
<code java>
package chapter06;
 
public class ArrEx1 {
 
    public static void main(String[] args) {
         
        int[] arrInt;
        int arrInt2[] = null;
         
        //System.out.println(arrInt[0]); // 에러 발생
        System.out.println(arrInt2[0]); // 에러 발생하지 않음
         
 
    }
 
}

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package chapter06;
 
public class ArrEx2 {
 
    public static void main(String[] args) {
         
        int[] arrInt = new int[5]; // 길이가 5개인 배열 객체 생성
         
        System.out.println(arrInt[0]);
 
    }
 
}

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package chapter06;
 
public class ArrEx3 {
 
    public static void main(String[] args) {
         
        int[] arrInt = new int[5]; // 길이가 5개인 배열 객체 생성
         
        arrInt[0] = 1;
        arrInt[1] = 2;
        arrInt[2] = 3;
        arrInt[3] = 4;
        arrInt[4] = 5;
         
    }
 
}

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package chapter06;
 
public class ArrEx4 {
 
    public static void main(String[] args) {
         
        String[] arrStr = new String[5];
         
//      System.out.println(arrStr[0]);
         
        char[] arrChar = new char[3];
        System.out.print(arrChar[0]*2);
        System.out.print('\u0000'*2);
         
    }
 
}

배열 사용

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package chapter06;
 
public class ArrEx5 {
 
    public static void main(String[] args) {
         
        String[] arrStr = {"홍길동", "이순신", "김유신"};
         
         
    }
 
}

배열 사용

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package chapter06;
 
public class ArrEx6 {
 
    public static void main(String[] args) {
         
        String[] arrStr = {"홍길동", "이순신", "김유신"};
         
        System.out.println("배열의 길이 : "+arrStr.length);
         
    }
 
}

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package chapter06;
 
public class ArrEx7 {
 
    public static void main(String[] args) {
         
        String[] arrStr = {"홍길동", "이순신", "김유신"};
         
        for (int i=0; i<arrStr.length; i++) {
            System.out.println(arrStr[i]);
        }
         
    }
 
}

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package chapter06;
 
public class ArrEx8 {
 
    public static void main(String[] args) {
         
        int[] number = new int[100];
         
        // 배열 변수에 대입
        for (int i=0; i<number.length; i++) {
            number[i] = i+1;
        }
         
        // 배열 변수 출력
        for (int i=0; i<number.length; i++) {
            System.out.println(number[i]);
        }
         
    }
 
}

로또번호 자동 추출기

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package chapter06;
 
public class Lotto {
 
    public static void main(String[] args) {
         
        int[] lotto = new int[6];
         
        int idx = 0;
        while (true) {
            int number = (int)(Math.random()*45)+1;
             
            boolean insert = true;
            for (int i=0; i<=idx; i++) {
                if (lotto[i] == number) {
                    insert = false;
                    break;
                }
            }
            if (insert == true) {
                lotto[idx] = number;
                idx++;
            }
             
            if (idx == 6) break;
        }
         
        for (int i=0; i<lotto.length; i++) {
            System.out.println(lotto[i]);
        }
         
    }
 
}

args 변수의 배열에 값 입력

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package chapter06;
 
public class ArrEx9 {
 
    public static void main(String[] args) {
         
        System.out.println("첫번째 값 : "+args[0]);
        System.out.println("두번째 값 : "+args[1]);
         
    }
 
}

다차원 배열

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package chapter06;
 
public class ArrEx10 {
 
    public static void main(String[] args) {
         
        // 첫번째
        int[][] matrix = new int[3][3];
         
        matrix[0][0] = 1;
        matrix[0][1] = 2;
        matrix[0][2] = 3;
        matrix[1][0] = 4;
        matrix[1][1] = 5;
        matrix[1][2] = 6;
        matrix[2][0] = 7;
        matrix[2][1] = 8;
        matrix[2][2] = 9;
         
        // 두번째
        int[][] matrix2 = {{1,2,3}, {4,5,6}, {7,8,9}};
         
        // 세번째
        int[][] matrix3 = {
                {1,2,3},
                {4,5,6},
                {7,8,9}
        };
         
        System.out.println("[첫번째]");
        for (int i=0; i<matrix.length; i++) {
            for (int j=0; j<matrix[i].length; j++) {
                System.out.print(matrix[i][j]+" ");
            }
            System.out.println();
        }
        System.out.println("[두번째]");
        for (int i=0; i<matrix2.length; i++) {
            for (int j=0; j<matrix2[i].length; j++) {
                System.out.print(matrix2[i][j]+" ");
            }
            System.out.println();
        }
        System.out.println("[세번째]");
        for (int i=0; i<matrix3.length; i++) {
            for (int j=0; j<matrix3[i].length; j++) {
                System.out.print(matrix3[i][j]+" ");
            }
            System.out.println();
        }
         
         
    }
 
}

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package chapter06;
 
public class ArrEx11 {
 
    public static void main(String[] args) {
         
        int[][][] arrInt = new int[3][3][3];
         
        int value = 0;
        // 값 대입
        for (int i=0; i<=2; i++) {
            for (int j=0; j<=2; j++) {
                for (int k=0; k<=2; k++) {
                    arrInt[i][j][k] = value++;
                }
            }
        }
         
        // 값 출력
        for (int i=0; i<=2; i++) {
            for (int j=0; j<=2; j++) {
                for (int k=0; k<=2; k++) {
                    System.out.print(arrInt[i][j][k]+"\t");
                }
                System.out.println();
            }
        }
         
         
    }
 
}

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package chapter06;
 
public class ArrEx12 {
 
    public static void main(String[] args) {
         
        int[][] arrInt = new int[3][];
         
        arrInt[0] = new int[] {1};
        arrInt[1] = new int[] {2,3};
        arrInt[2] = new int[] {4,5,6};
         
        for (int i=0; i<arrInt.length; i++) {
            for (int j=0; j<arrInt[i].length; j++) {
                System.out.print(arrInt[i][j]);
            }
            System.out.println();
        }
         
         
    }
 
}

배열 복사

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package chapter06;
 
public class ArrEx13 {
 
    public static void main(String[] args) {
         
        // 원본 배열
        int[] arrInt = {1,2,3};
         
        // 복사할 배열
        int[] arrInt2 = new int[5];
         
        // 복사할 배열에 값 대입
        for (int i=0; i<arrInt.length; i++) {
            arrInt2[i] = arrInt[i];
        }
         
        // 배열 값 출력
        for (int i=0; i<arrInt2.length; i++) {
            System.out.println(arrInt2[i]);
        }
         
    }
 
}

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package chapter06;
 
public class ArrEx14 {
 
    public static void main(String[] args) {
         
        // 원본 배열
        int[] arrInt = {1,2,3};
         
        // 복사할 배열
        int[] arrInt2 = new int[5];
         
        System.arraycopy(arrInt, 0, arrInt2, 2, arrInt.length);
         
        // 배열 값 출력
        for (int i=0; i<arrInt2.length; i++) {
            System.out.println(arrInt2[i]);
        }
         
    }
 
}

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package chapter06;
 
import java.util.Arrays;
 
public class ArrEx15 {
 
    public static void main(String[] args) {
         
        // 원본 배열
        int[] arrInt = {1,2,3};
         
        // 복사할 배열
        int[] arrInt2 = null;
         
        arrInt2 = Arrays.copyOf(arrInt, 5);
         
        // 배열 값 출력
        for (int i=0; i<arrInt2.length; i++) {
            System.out.println(arrInt2[i]);
        }
         
    }
 
}

향상된 for 문

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package chapter06;
 
public class ArrEx16 {
 
    public static void main(String[] args) {
         
        // 배열
        int[] arrInt = {1,2,3,4,5};
         
        // 기존 for문을 이용한 출력
        for (int i=0; i<arrInt.length; i++) {
            System.out.println(arrInt[i]);
        }
         
        // 향상된 for문을 이용한 출력
        for (int number : arrInt) {
            System.out.println(number);
        }
         
    }
 
 
}

참조자료형

값이 아닌 메모리 주소를 비교

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package chapter06;
 
public class ReferenceType {
 
    public static void main(String[] args) {
         
        String name1 = "홍길동";
        String name2 = "홍길동";
         
        System.out.println(name1 == name2);
 
    }
 
}

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package chapter06;
 
public class ReferenceType2 {
 
    public static void main(String[] args) {
         
        String name1 = new String("홍길동");
        String name2 = new String("홍길동");
         
        System.out.println(name1 == name2);
 
    }
 
}

==연산자 가 아닌 equals() 메서드를 사용 (문자열값 자체를 비교)

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package chapter06;
 
public class ReferenceType3 {
 
    public static void main(String[] args) {
         
        String name1 = new String("홍길동");
        String name2 = new String("홍길동");
         
        System.out.println(name1.equals(name2));
 
    }
 
}
배열 객체로 비교
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package chapter06;
 
import java.util.Arrays;
 
public class ReferenceType4 {
 
    public static void main(String[] args) {
         
        // 배열 변수 생성
        int[] arr1 = {1,2,3};
        int[] arr2 = {1,2,3};
         
        System.out.println("arr1 == arr2 : " + (arr1 == arr2));
         
        int[] arr3 = arr1;
        System.out.println("arr1 == arr3 : " + (arr1 == arr3));
         
        arr3[0] = 4;
        System.out.println("arr3[0] : "+arr3[0]);
        System.out.println("arr1[0] : "+arr1[0]);
         
    }
 
}

배열 객체 값을 그대로 받으면서 별개의 주소값을 갖는 참조자료형 만들기

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package chapter06;
 
import java.util.Arrays;
 
public class ReferenceType5 {
 
    public static void main(String[] args) {
         
        // 배열 변수 생성
        int[] arr1 = {1,2,3};
         
        int[] arr2 = Arrays.copyOf(arr1, 3);
         
        arr2[0] = 4;
        System.out.println("arr1[0] : "+arr1[0]);
        System.out.println("arr2[0] : "+arr2[0]);
         
    }
 
}

마지막으로 수정됨: 2025/06/27 16:06
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