개발새발 IT

public class dailyCode {

static{

//once run

System.out.println("run when start program");

}

{

//whenever create instance

System.out.println("run when create instance");

}

public static void main(String[] args){

System.out.println("run main");

dailyCode test1 = new dailyCode();

dailyCode test2 = new dailyCode();

}

} 

import java.util.HashSet;;

public class dailyCode {

public static void main(String[] args){

HashSet set = new HashSet();

HashSet setCopy = new HashSet();

set.add("one");//autoboxing

set.add("one");

set.add("two");

set.add("one");

set.add(new String("three"));//Wrapper class

set.add(1);

set.add(100.5);

System.out.println("set : " + set.toString());

setCopy.addAll(set);

System.out.println("setCopy : " + setCopy.toString());

set.remove("one");

System.out.println("set : " + set.toString());

setCopy.clear();

System.out.println("setCopy : " + setCopy.toString());

}

} 

import java.util.ArrayList;

public class dailyCode {

public static void main(String []args){

ArrayList list = new ArrayList<>();

String[] add = new String[5];

int i = 0;

for(String str : add){

str = "add" + i++;

list.add(str);

}

for(int j=0; j<list.size(); j++){

System.out.println(list.get(j));

}

list.set(0, "set0");

list.remove(3);

list.remove("add4");

System.out.println("----");

for(int j=0; j<list.size(); j++){

System.out.println(list.get(j));

}

}

}