자바의 정석 / Chap9) java.lang패키지와 유용한 클래스 - 연습문제

9-1)

package j17_Lambda;

import java.util.Arrays;

class SutdaCard {
	int num;
	boolean isKwang;
	
	SutdaCard() {
		this(1, true);
	}
	
	SutdaCard(int num, boolean isKwang) {
		this.num = num;
		this.isKwang = isKwang;
	}
	
	public boolean equals(Object obj) {
		if (obj instanceof SutdaCard) {
			SutdaCard c = (SutdaCard)obj;
			return num == c.num && isKwang == c.isKwang;
		} else {
			return false;
		}
	}
	
	public String toString() {
		return num + (isKwang ? "k" : "");
	}
}

public class Ex_chapter9 {

	public static void main(String[] args) {
		SutdaCard c1 = new SutdaCard(3, true);
		SutdaCard c2 = new SutdaCard(3, true);
		
		System.out.println("c1 = " + c1);
		System.out.println("c2 = " + c2);
		System.out.println("cl.equals(c2) : " + c1.equals(c2));
	}

}

 

 

9-2)

package j17_Lambda;

class Point3D {
	int x, y, z;
	
	Point3D (int x, int y, int z) {
		this.x = x;
		this.y = y;
		this.z = z;
	}
	
	Point3D() {
		this(0 ,0 ,0);
	}
	
	public boolean equals(Object obj) {
		if (obj instanceof Point3D) {
			Point3D p = (Point3D) obj;
			return x == p.x && y == p.y && z == p.z;
		} else {
			return false;
		}
	}
	
	public String toString() {
		return "[" + x + ", " + y + ", " + z + "]";
	}
	
}

public class Ex_chapter9 {

	public static void main(String[] args) {
		Point3D p1 = new Point3D(1, 2, 3);
		Point3D p2 = new Point3D(1, 2, 3);
		
		System.out.println(p1);
		System.out.println(p2);
		System.out.println("p1 == p2 ? " + (p1 == p2));
		System.out.println("p1.equals(p2) ? " + (p1.equals(p2)));
	}
}

 

 

9-3)

package example01;

public class Ex_chapter9 {
	public static int count(String src, String target) {
		int count = 0;
		int pos = 0;

		while (true) {
			int res = src.indexOf(target, pos);

			if (res == -1) {
				return count;
			} else {
				count++;
				pos += target.length();
			}
			return count;
		}
	}

	public static void main(String[] args) {
		System.out.println(count("12345AB12AB345AB", "AB"));
		System.out.println(count("12345", "AB"));
	}

}

내가 처음 작성한 코드이다.

res라는 변수를 추가해서 target의 위치를 반환받고 있다.

하지만 애초에 따로 변수를 선언하지 않고 처음부터 pos에 첫 위치를 담으면 되는 것이었다.

아래는 수정한 코드이다.

 

package example01;

public class Ex_chapter9 {
	public static int count(String src, String target) {
		int count = 0;
		int pos = 0;

		while (true) {
			pos = src.indexOf(target, pos);

			if (pos != -1) {
				count++;
				pos += target.length();
			} else {
				break;
			}
		}
		return count;
	}

	public static void main(String[] args) {
		System.out.println(count("12345AB12AB345AB", "AB"));
		System.out.println(count("12345", "AB"));
	}

}

 

 

9-4)