[Java] 생활코딩 JAVA 객체 지향 프로그래밍

[생활코딩 JAVA 객체 지향 프로그래밍]

Ⅱ. 남의 클래스 & 남의 인스턴스

package projectOOP;

import java.io.FileWriter;
import java.io.IOException;

public class OthersOOP {

	public static void main(String[] args) throws IOException {
		
		System.out.println(Math.PI); // 3.14웅앵웅
		System.out.println(Math.floor(1.8)); // 내림
		System.out.println(Math.ceil(1.8)); // 올림
		
		FileWriter f1 = new FileWriter("data.txt");
		f1.write("Hello");
		f1.write(" Java");
		f1.close();
	}

}

실행 결과

data.txt 파일에

Hello Java가 쓰여 있다.

---

Ⅲ. 변수와 메소드

블럭 씌워서 선택 후 우클릭 → Refactor → Extract Method...

메서드명 입력 → public 선택 → OK.

메서드가 자동으로 만들어진다.

package projectOOP;

public class MyOOP {
	
	public static void main(String[] args) {
		delimiter = "---";
		printA();
		printB();
		
		delimiter = "***";
		printA();
		printB();
	}

	public static String delimiter = "";
	
	public static void printA() {
		System.out.print(delimiter);
		System.out.print("A");
		System.out.println("A");
	}
	
	public static void printB() {
		System.out.print(delimiter);
		System.out.print("B");
		System.out.println("B");
	}

}

---

Ⅳ. 클래스

Ⅲ에서 했던 것처럼 역시 메서드 선택 → 우클릭 → Refactor → Move Type to New File...

Print 클래스를 따로 파일로 뺐다.

public class MyOOP {
    public static void main(String[] args) {
        Print.delimiter = "---";
        Print.A();
        Print.B();
 
        Print.delimiter = "***";
        Print.A();
        Print.B();
    }
}

class Print {
    public static String delimiter = "";
 
    public static void A() {
        System.out.println(delimiter);
        System.out.println("A");
        System.out.println("A");
    }
 
    public static void B() {
        System.out.println(delimiter);
        System.out.println("B");
        System.out.println("B");
    }
}

---

Ⅴ. 인스턴스

package projectOOP;

public class MyOOP {
	
	public static void main(String[] args) {
		
		Print p1 = new Print();
		p1.delimiter = "---";
		p1.A();
		p1.B();
		
		Print p2 = new Print();
		p2.delimiter = "***";
		p2.A();
		p2.B();
	}

}

package projectOOP;

class Print {

public static String delimiter = "";
	
	public void A() {
		System.out.print(delimiter);
		System.out.print("A");
		System.out.println("A");
	}
	
	public void B() {
		System.out.print(delimiter);
		System.out.print("B");
		System.out.println("B");
	}

}

---

Ⅵ. static

package projectOOP;

class Foo {
	
	public static String classVar = "I class var";
	public String instanceVar = "I instance var";
	public static void classMethod() {
		System.out.println(classVar);	 // 접근 가능
//		System.out.println(instanceVar); // 접근 불가
	}
	
	public void instanceMethod() {
		System.out.println(classVar);	 // 접근 가능
		System.out.println(instanceVar); // 접근 가능
	}
}

public class StaticApp {

	public static void main(String[] args) {
		System.out.println(Foo.classVar);	 // 접근 가능
//		System.out.println(Foo.instanceVar); // 접근 불가
		Foo.classMethod();	  // 접근 가능
//		Foo.instanceMethod(); // 접근 불가
		
		Foo f1 = new Foo();
        Foo f2 = new Foo();

        System.out.println(f1.classVar);	// I class var
        System.out.println(f1.instanceVar); // I instance var

        f1.classVar = "changed by f1";
        System.out.println(Foo.classVar); // changed by f1
        System.out.println(f2.classVar);  // changed by f1

        f1.instanceVar = "changed by f1";
        System.out.println(f1.instanceVar); // changed by f1
        System.out.println(f2.instanceVar); // I instance var
    }

}

---

Ⅶ. 생성자와 this

package projectOOP;

public class MyOOP {
	
	public static void main(String[] args) {
		
		Print p1 = new Print("---");
//		p1.A();
//		p1.B();
//		
//		Print p2 = new Print("***");
//		p2.A();
//		p2.B();
	}

}

package projectOOP;

class Print { // Print 클래스 파일로 따로 분리함.

	public static String delimiter = "";
	
	public Print(String delimiter) {
		this.delimiter = delimiter;
	}
	
	public void A() {
		System.out.print(this.delimiter);
		System.out.print("A");
		System.out.println("A");
	}
	
	public void B() {
		System.out.print(this.delimiter);
		System.out.print("B");
		System.out.println("B");
	}

}

---

Ⅷ. 활용

1. 클래스화

package projectMethod;

class Accounting { // 클래스로 연관된 메소드끼리 정리정돈.
	
    public static double valueOfSupply = 10000.0;
    public static double vatRate = 0.1;
 
    public static double getVAT() {
        return valueOfSupply * vatRate;
    }
    
    public static double getTotal() {
        return valueOfSupply + getVAT();
    }
    
}

public class AccountingApp {

    public static void main(String[] args) {
 
        System.out.println("Value of supply : " + Accounting.valueOfSupply);
        System.out.println("VAT : " + Accounting.getVAT());
        System.out.println("Total : " + Accounting.getTotal());
    }

}

2. 인스턴스화

package projectMethod;

class Accounting { // 클래스로 연관된 메소드끼리 정리정돈.
	
	public double valueOfSupply;
    public static double vatRate = 0.1;
    
    public Accounting(double valueOfSupply) {
    	this.valueOfSupply = valueOfSupply;
    }
 
    public double getVAT() {
        return valueOfSupply * vatRate;
    }
    
    public double getTotal() {
        return valueOfSupply + getVAT();
    }
    
}

public class AccountingApp {

    public static void main(String[] args) {
    	
    	Accounting a1 = new Accounting(10000.0);
    	Accounting a2 = new Accounting(20000.0);
    	
        System.out.println("Value of supply : " + a1.valueOfSupply);
        System.out.println("Value of supply : " + a2.valueOfSupply);
        System.out.println("VAT : " + a1.getVAT());
        System.out.println("VAT : " + a2.getVAT());
        System.out.println("Total : " + a1.getTotal());
        System.out.println("Total : " + a2.getTotal());
    }

}

 

출처 : 

JAVA 객체지향 프로그래밍