Java - Code Sample

/* 01 - Reference */
package package_01;

public class TestClass{
	private int a;
	public void set(int a) {
		this.a = a;
	}
	public void add(int d) {
		a += d;
	}
	public void print() {
		System.out.println(a);
	}
	public static void main(String args[]) {
		TestClass p = new TestClass();
		TestClass q;
		p.set(10);
		q = p;
		p.add(10);
		q.set(30);
		p.print();
	}
}

/* 02 - Constructor */
package package_01;

class Ref{
	int a;
	Ref(int x){
		a = x;
	}
	
	int sum(Ref obj) {
		int k;
		k = obj.a - a;
		a = 10;
		obj.a = 20;
		return k;
	}
}

class TestClass{
	public static void main(String args[]) {
		Ref obj1 = new Ref(3);
		Ref obj2 = new Ref(4);
		int k1 = obj2.sum(obj1);
		System.out.print(" k1 = " +k1);
		System.out.print(" obj1.a= " +obj1.a);
		System.out.print(" obj2.a= " +obj2.a);
	}
}

// k1 = -1 obj1.a= 20 obj2.a= 10

/* 03 - Access Modifier */
package package_01;

class Person{
	private String name;
	public int age;
	public void setAge(int age) {
		this.age = age;
	}
	public String toString() {
		return("name: " + this.name + ", age: " + this .age);
	}
}

class TestClass{
	public static void main(String[] args) {
		Person a = new Person();
		a.setAge(27);
//		a.name = "Jake";
		
		System.out.println(a);
	}
}

//name: null, age: 27

/* 04- Inheritance */

class C {}
class CS extends C {}
interface I {}
class CI extends C implements I {}

public class TestClass{
	public static void main(String args[]) {
		static I i = new CI();
		static C ca = new CI();
//		static CS cs = new C();
		static C cb = new CS();
	}
}

/*
 *  C - CS - static C cb
 *    - CI - static I i
 *         - static C ca
 *  ㄴ static CS cs (x)
 */

/* 05- Access, Inheritance */

class A1{
	public int x;
	private int y;
	protected int z;
}

class A2 extends A1{
	protected int a;
	private int b;
}

class A3 extends A2{
	private int q;
	// x, z, a, q
}

/* 06 - Inheritance  */

class Subject1{
	protected int a = 1000;
	public int fun1() {
		return a;
	}
}

class Subject2 extends Subject1{
	private int b = 5;
	public int fun2() {
		return a/b;
	}
}

public class TestClass{
	public static void main(String[] args) {
		Subject2 sub = new Subject2();
		System.out.println(sub.fun1());
		System.out.println(sub.fun2());
	}
}

//1000
//200

/* 07 - Inheritance, super()  */

class A{
	A(){
		System.out.printf("%d ", 10);
	}
}

class B extends A{
	B(int a){
		System.out.printf("%d ", a);
	}
}

class C extends B{
	C(int a){
		super(a/10);
		System.out.printf("%d ", a);
	}
}

public class TestClass{
	public static void main(String[] args) {
		A b = new C(1000);
	}
}

// 10 100 1000

/* 08 - Inheritance, Constructor, super() */

class A{
	int a;
	A(int a){
		this.a = a;	// Constructor
	}
	void display() {
		System.out.println("a="+a);
	}
}

class B extends A{
	B(int a){	// Constructor
		super(a);
		super.display();
	}
}

public class TestClass{
	public static void main(String[] args) {
		B obj = new B(10);
	}
}

// a = 10

/* 09 - Inheritance, super()  */

class AA{
	int d1;
	int s;
	AA(int s1){
		s = s1;
		d1 = s * s;
	}
}

class BB extends AA{
	int d2;
	int t;
	BB(int s1, int t1){
		super(s1);
		t = t1;
		d2 = t * t;
	}
}

class TestClass{
	public static void main(String[] args) {
		BB myTest = new BB(10, 20);
		System.out.println("Result1: " + myTest.d1);
		System.out.println("Result2: " + myTest.d2);
	}
}

//Result1: 100
//Result2: 400

/* 10 - Inheritance, super()  */

class Super{
	Super(){
		System.out.print('A');	// 4 (A)
	}
	Super(char x){
		System.out.print(x);	// 1 (C)
	}
}

class Sub extends Super{
	Sub(){
		super();				// 3
		System.out.print('B');	// 5 (B)
	}
	Sub(char x){
		this();					// 2
		System.out.print(x);	// 6 (D)
	}
}

class TestClass{
	public static void main(String[] args) {
		Super s1 = new Super('C');
		Super s2 = new Sub('D');
	}
}

// CABD

/* 11 - Inheritance, constructor  */

class TestClass{
	int a = 10;
	public TestClass() {
		System.out.print("가");
	}
	public TestClass(int x) {
		System.out.print("나");
	}
	public static void main(String[] args) {
		B b1 = new B();
		TestClass b2 = new B(1);
		System.out.print(b1.a + b2.a);
	}
}

class B extends TestClass{
	int a = 20;
	public B() {
		System.out.print("다");
	}
	public B(int x) {
		System.out.print("라");
	}
}

// 가다가라30

/* 12 - Overloading  */

class TestClass{
	void f() {
		System.out.println("0");
	}
	
	void f(int i) {
		System.out.println(i);
	}
	void f(int i, int j) {
		System.out.println(i+j);
	}
	public static void main(String[] args) {
		TestClass a = new TestClass();
		a.f(25, 25);
	}
}

// 50