'Back-End/Java_1'에 해당되는 글 48건

Aggregation in java

- If a class have an entity reference, It is known as Aggregation

1. Why use Aggregation

- For code Reuseability

2. Example

1) Address.java

public class Address { String city, state, country; public Address(String city, String state, String country){ this.city = city; this.state = state; this.country = country; } }

2) Emp.java

public class Emp { int id; String name; Address address; public Emp(int id,String name, Address address){ this.id = id; this.name = name; this.address = address; } void display(){ System.out.println(id + name); System.out.println(address.city + address.country); } public static void main(String[]args){ Address ad1 = new Address("seoul","Up","kor"); Emp e1 = new Emp(111,"KYLE",ad1); e1.display(); } }  

Inheritance in Java

- Inheritance is a mechanism in which on object acquires all the properties and behaviors of parent object

- For method Overriding(so runtime polymorphism can be achieved)

- For code reusability

1. Example

class Test1{ float salary = 40000; } public class Test extends Test1{ int bonus = 10000; public static void main(String[]args){ Test a = new Test(); System.out.println(a.salary); System.out.println(a.bonus); } }

2. Why multiple inheritance is not supported in java?

- To reduce the complexity and simplify the language

Input by Console

- The Java Console class is used to get input from console

- It provides methods to read text and password

- If you read password using console, it will not be displayed to the user

1. Method of Console class

2. Example

public static void main(String[]args){ Console c = System.console(); System.out.println("Enter name"); String n = c.readLine(); System.out.println("Welcome"+n); char[] ch = c.readPassword(); String pass = String.valueOf(ch); System.out.println("Pass"+pass); }

 Input by BufferedReader

1. Reading data from keyboard

- There are many ways to read data from keyboard

1) InputStreamReader

2) Console

3) Scanner

4) DataInputStream etc..

2. InputStreamReader class

- InputStreamReader class can be used to read data from keyboard. It performs two tasks

1) connects to input stream of keyboard

2) converts the byte-oriented stream into character-oriented stream

3. BufferedReader class

- BufferedReader class can be used to read data by line by readLine() method

4. Example

1) Simple

public class FourOperation { public static void main(String[]args) throws IOException{ InputStreamReader r = new InputStreamReader(System.in); BufferedReader br = new BufferedReader(r); System.out.println("Enter your name"); String name = br.readLine(); System.out.println("Welcome" + name); } }

2) User can stop the program

package output; import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; public class FourOperation { public static void main(String[]args) throws IOException{ InputStreamReader r = new InputStreamReader(System.in); BufferedReader br = new BufferedReader(r); String name=""; while(!name.equals("stop")){ System.out.println("Enter your name"); name = br.readLine(); System.out.println("Welcome" + name); } br.close(); r.close(); } }