KU COSE102 2019기말고사 복습 Part 1

KU COSE102 2019 기말고사 복습 Part 1

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객체지향 프로그래밍 Object Oriented Programming (OOP)

JAVA 09

Object-oriented programming (OOP) involves programming using objects.

클래스와 객체 Class and Object

JAVA 10

A class defines the properties and behaviors for objects.

An object represents an entity in the real world that can be distinctly identified.

For example, a student, a desk, a circle, a button, and even a loan can all be viewed as objects.

An object has a unique identity, state, and behavior.

생성자 Constructor

JAVA 10

A constructor is invoked to create an object using the new operator.

A constructor must have the same name as the class itself.

Constructors do not have a return type—not even void.

Constructors are invoked using the new operator when an object is created. Constructors play the role of initializing objects.

Date Class

JAVA 42

Random Class

JAVA 20

Random r = new Random();
r.nextInt(); //random integer
r.nextInt(int n); //random integer between 0~n, excluding n
r.nextLong(); //random long
r.nextDouble(); //random double between 0.0~1.0, excluding 1.0
r.nextFloat(); //random float between 0.0F~1.0F, excluding 1.0F
r.nextBoolean(); //random boolean value

static

JAVA 13

A static variable is shared by all objects of the class.

A static method cannot access instance members of the class.

Access Modifier (Visibility Modifier)

JAVA 12

Visibility modifiers can be used to specify the visibility of a class and its members.

멤버에 접근하는 클래스	private	default	protected	public
같은 패키지의 클래스	X	O	O	O
다른 패키지의 클래스	X	X	X	O
접근 가능 영역	클래스 내	동일 패키지 내	동일 패키지와 자식 클래스	모든 클래스

Array of Objects

JAVA 11

this

JAVA 10

The keyword this refers to the object itself.

It can also be used inside a constructor to invoke another constructor of the same class.

Wrapper Class

JAVA 19

A primitive type value is not an object, but it can be wrapped in an object using a wrapper class in the Java API.

A primitive type value can be automatically converted to an object using a wrapper class, and vice versa, depending on the context.

BigInteger Class

The BigInteger and BigDecimal classes can be used to represent integers or decimal numbers of any size and precision.

import java.math.*; 필요

import java.math.*;

public class Main {
    public static void main(String[] args) {
        BigInteger a = new BigInteger("12313434247874365645");
        BigInteger b = new BigInteger("4641351341341141");

        BigInteger sum = a.add(b);
        BigInteger sub = a.subtract(b);
        BigInteger mul = a.multiply(b);
        BigInteger div = a.divide(b);
        BigInteger rem = a.remainder(b);
        BigInteger one = BigInteger.ONE;

        System.out.println(a);
        System.out.println(b);
        System.out.println(sum);
        System.out.println(sub);
        System.out.println(mul);
        System.out.println(div);
        System.out.println(rem);
        System.out.println(one);
    }
}

출력결과

12313434247874365645
4641351341341141
12318075599215706786
12308792896533024504
57150974562887630658699188915500945
2652
4570490637659713
1

String Class

JAVA 20

A String object is immutable: Its content cannot be changed once the string is created.