[JAVA] 배열 예제

public class AdvancedForExample {

	public static void main(String[] args) {
		// TODO Auto-generated method stub

		int[] scores = {95, 71, 84, 93, 87};
		
		int sum = 0;
		for(int score : scores) {
			sum = sum + score;
		}
		System.out.println("점수 총합 = " + sum);
		
		double avg = (double)sum / scores.length;
		System.out.println("점수 평균 = " + avg);
	}

}

public class ArrayCopyByForExample {

	public static void main(String[] args) {
		// TODO Auto-generated method stub

		int[] oldIntArray = {1, 2, 3};
		int[] newIntArray = new int[5];
		
		for(int i = 0; i < oldIntArray.length; i++) {
			newIntArray[i] = oldIntArray[i];
		}
		
		for(int i = 0; i < newIntArray.length; i++) {
			System.out.print(newIntArray[i] + ", ");	// 1, 2, 3, 0, 0,	: int 배열의 초기값은 0
		}
	}

}

public class ArrayCopyExample {

	public static void main(String[] args) {
		// TODO Auto-generated method stub

		String[] oldStrArray = {"java", "array", "copy"};
		String[] newStrArray = new String[5];
		
		System.arraycopy(oldStrArray, 0, newStrArray, 0, oldStrArray.length);
		
		for(int i = 0; i < newStrArray.length; i++) {
			System.out.print(newStrArray[i] + ", ");	// java, array, copy, null, null,
		}
	}

}

public class ArrayCreateByNewExample {

	public static void main(String[] args) {
		// TODO Auto-generated method stub

		int[] arr1 = new int[3];
		for(int i = 0; i < 3; i++) {
			System.out.println("arr1[" + i + "] : " + arr1[i]);
		}
		
		arr1[0] = 10;
		arr1[1] = 20;
		arr1[2] = 30;
		
		for(int i = 0; i < 3; i++) {
			System.out.println("arr1[" + i + "] : " + arr1[i]);
		}
		
		double[] arr2 = new double[3];
		for(int i = 0; i < 3; i++) {
			System.out.println("arr2[" + i + "] : " + arr2[i]);
		}
		
		arr2[0] = 0.1;
		arr2[1] = 0.2;
		arr2[2] = 0.3;
		
		for(int i = 0; i < 3; i++) {
			System.out.println("arr2[" + i + "] : " + arr2[i]);
		}
		
		String[] arr3 = new String[3];
		for(int i = 0; i < 3; i++) {
			System.out.println("arr3[" + i + "] : " + arr3[i]);
		}
		
		arr3[0] = "1월";
		arr3[1] = "2월";
		arr3[2] = "3월";
		
		for(int i = 0; i < 3; i++) {
			System.out.println("arr3[" + i + "] : " + arr3[i]);
		}
	}

}

public class ArrayCreateByValueListExample1 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub

		int[] scores = {83, 90, 87};
		
		System.out.println("score[0] : " + scores[0]);	// 83
		System.out.println("score[1] : " + scores[1]);	// 90
		System.out.println("score[2] : " + scores[2]);	// 87
		
		int sum = 0;
		for(int i = 0; i < 3; i++) {
			sum += scores[i];
		}
		System.out.println("총합 : " + sum);	// 총합 : 260
		
		double avg = (double)sum /3;
		System.out.println("평균 : " + avg);	// 평균 : 86.6666666666667
	}

}

public class ArrayCreateByValueListExample2 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub

		int[] scores;
		scores = new int[] {83, 90, 87};
		int sum1 = 0;
		
		for(int i = 0; i < 3; i++) {
			sum1 += scores[i];
		}
		System.out.println("총합 : " + sum1);
		
		int sum2 = add(new int[] {83, 90, 87});
		System.out.println("총합 : " + sum2);
		System.out.println();
	}
	
	public static int add(int[] scores) {
		int sum = 0;
		for(int i = 0; i < 3; i++) {
			sum += scores[i];
		}
		return sum;
	}

}

public class ArrayInArrayExample {

	public static void main(String[] args) {
		// TODO Auto-generated method stub

		int[][] mathScores = new int[2][3];
		for(int i = 0; i < mathScores.length; i++) {
			for(int k = 0; k < mathScores.length; k++) {
				System.out.println("mathScores[" + i + "][" + k + "] = " + mathScores[i][k]);
			}
		}
		System.out.println();
		
		int[][] englishScores = new int[2][];
		englishScores[0] = new int[2];
		englishScores[1] = new int[3];
		for(int i = 0; i < englishScores.length; i++) {
			for(int k = 0; k < englishScores.length; k++) {
				System.out.println("englishScores[" + i + "][" + k + "] = " + englishScores[i][k]);
			}
		}
		System.out.println();
		
		int[][] javaScores = {{95, 80}, {92, 96, 80}};
		for(int i = 0; i < javaScores.length; i++) {
			for(int k = 0; k < javaScores.length; k++) {
				System.out.println("javaScores[" + i + "][" + k + "] = " + javaScores[i][k]);
			}
		}
	}

}

public class ArrayLengthExample {

	public static void main(String[] args) {
		// TODO Auto-generated method stub

		int[] scores = {83, 90, 87};
		
		int sum = 0;
		for(int i = 0; i < scores.length; i++) {
			sum += scores[i];
		}
		System.out.println("총합 : " + sum);
		
		double avg = (double)sum / scores.length;
		System.out.println("평균 : " + avg);
	}

}

public class ArrayReferenceObjectExample {

	public static void main(String[] args) {
		// TODO Auto-generated method stub

		String[] strArray = new String[3];
		strArray[0] = "Java";
		strArray[1] = "Java";
		strArray[2] = new String("Java");
		
		System.out.println(strArray[0] == strArray[1]);	// true	: 동일한 String 객체를 참조하기 때문
		System.out.println(strArray[0] == strArray[2]);	// false	: new 연산자로 객체 생성하면 새로운 String 객체 생성되기 때문
		System.out.println(strArray[0].equals(strArray[2]));	// true	: 문자열을 비교하기 때문
	}

}

public class StringEqualsExample {

	public static void main(String[] args) {
		// TODO Auto-generated method stub

		String strVar1 = "이현경";
		String strVar2 = "이현경";
		
		if(strVar1 == strVar2) {
			System.out.println("strVar1과 strVar2는 참조가 같음");
		} else {
			System.out.println("strVar1과 strVar2는 참조가 다름");
		}
		
		if(strVar1.equals(strVar2)) {
			System.out.println("strVar1과 strVar2는 문자열이 같음");
		}
		
		String strVar3 = new String("이현경");
		String strVar4 = new String("이현경");
		
		if(strVar3 == strVar4) {
			System.out.println("strVar3과 strVar4는 참조가 같음");
		} else {
			System.out.println("strVar3과 strVar4는 참조가 다름");
		}
		
		if(strVar3.equals(strVar4)) {
			System.out.println("strVar3과 strVar4는 문자열이 같음");
		}
	}

}