Java) Data Types

There are two data types in Java : Primitive and Reference.

They are the basic of basic in Java and very important to know to jump to the next step, so let's make them familiar!

Source : Javarevisted

 

Primitive Type

Type	Size	Description
byte	1 byte	Stores whole numbers from -128 to 127
short	2 bytes	Stores whole numbers from -32,768 to 32,767
int	4 bytes	Stores whole numbers from -2,147,483,648 to 2,147,483,647
long	8 bytes	Stores whole numbers from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
float	4 bytes	Stores fractional numbers. Sufficient for storing 6 to 7 decimal digits
double	8 bytes	Stores fractional numbers. Sufficient for storing 15 decimal digits
boolean	1 bit	Stores true or false values
char	2 bytes	Stores a single character/letter or ASCII values

Reference Type

Type	Description
Class	Describes the content of the object
Array	Stores the elements of the same type
Interface	A collection of abstract methods

The difference between Primitive and Reference Type is that

Source : Javarevisited

Variables 

Variable is a storage space for storing data on memor.

package p2022_06_21;

import java.util.ArrayList;

public class Variable {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		
		// 1. Integer Type
		byte b1 = 10; 			
		
		short s = 100; 
		
		int i = 1000; 
		long l = 100000L;  
		
		System.out.println("b1="+b1);
		System.out.println("s="+s);
		System.out.println("i="+i);
		System.out.println("l="+l);
		
		//2. Rational Type
		float ft1 = 3.14f;  
		// float ft1 = (float)3.14; 
		float ft2 = 3.14F; 
		double d = 42.195; 
		
		System.out.println("ft1="+ft1);
		System.out.println("ft2="+ft2);
		System.out.println("d="+d);
		
		
		System.out.printf("%.1f\n", d); 
		System.out.printf("%.2f", d); 
		System.out.printf("%.2f\n",d); 
		
		
		//3. Character Type
		char c1 = 'A';
		char c2 = '安'; 
		
		System.out.println("c1="+c1);
		System.out.println("c2="+c2);
		
		//4. Boolean Type
		boolean bn1 = true; 
		boolean bn2 = false;
		System.out.println("bn1="+bn1);
		System.out.println("bn2="+bn2);

		//Reference Type : Class
		String s1 = "Java";
		String s2 = new String("Java");
		
		System.out.println("s1="+s1);
		System.out.println("s2="+s2);
		if(s1 == s2){
			System.out.println("Same Address");
		} else {
			System.out.println("Different Address");
		}
		if(s1.equals(s2)){
			System.out.println("Same Value");
		} else {
			System.out.println("Different Value");
		}	
		
		//Reference variable : 배열- 동일한 자료형의 데이터를 저장하는 정적인 자료구조 
		int[] score = {80, 90, 100};
		
		for(int j=0; j<score.length; j++) {
			System.out.println(score[j]+"\t");
		}
		
		System.out.println();
			
		//Reference Type : Interface(List)
	
	  //List list = new List();  //Error 
		ArrayList list = new ArrayList(); //Upcasting
		list.add(30);
		list.add(3.14);
		list.add('j');
		list.add(true);
		list.add("Java");
		
		for(int k=0; k<list.size(); k++) {
		System.out.print(list.get(k)+"\t"); //\t는 insert a new tap 
		}

}

}