JAVA 06 배열/스트링/콜렉션

String을 사용 할 때는 == 사용금지

• 대신에 equals()를 사용

String str1 = "abcde";
String str2 = "abcde";
if (str1 == str2) {                 //주소
    System.out.println("같다");
} else {
    System.out.println("다르다");
}
 
if (str1.equals(str2)) {            //값
    System.out.println("같다");
} else {
    System.out.println("다르다");
}

String str3 = new String("abcde");
String str4 = new String("abcde");
if (str3 == str4) {                 //주소
    System.out.println("같다");
} else {
    System.out.println("다르다");
}
 
if (str3.equals(str4)) {            //값
    System.out.println("같다");
} else {
    System.out.println("다르다");
}

    

    

StringBuffer sb = new StringBuffer("abc");
System.out.println(sb);
sb.append("d"); 
System.out.println(sb);

    

    

System.out.println(str1.charAt(0));
System.out.println(str1.length());
System.out.println(str1.substring(0, 2));

String phon = "010-0000-7777";
String[] phonArr = phon.split("-");
 
for (int i = 0; i < phonArr.length; i++) {
    System.out.println(phonArr[i]);
}
 
System.out.println();

String phon1 = "021571577";
String[] phonArr1 = phon1.split("-");
 
for (int i = 0; i < phonArr1.length; i++) {
    System.out.println(phonArr1[i]);
}
 
String ch = phon1.replace("-", "");
System.out.println(ch);
 
String end = ch.substring(0, ch.length()-4);
System.out.println(end);
 
if(ch.substring(0, 2).equals("02")) {
    System.out.println(ch.substring(0, 2) + " " + end.substring(2) + " " + ch.substring(ch.length()-4, ch.length()));
} else {
    System.out.println(ch.substring(0, 3) + " " + end.substring(3) + " " + ch.substring(ch.length()-4, ch.length()));
}

int[][] score2 = new int[][] {
    {100, 90, 80},
    {80, 20, 30},
    {70, 90, 100},
    {30, 90, 60},
    {40, 100, 100}
};
 
System.out.println("번호\t총점"  );
System.out.println("=================");
for (int i = 0; i < score2.length; i++) {
    int sum2 = 0;
 
    System.out.print((i+1) + "\t");
    for (int j = 0; j < score2[i].length; j++) {
        sum2 += score2[i][j];
    }
    System.out.println(sum2);
}

int[][] score3 = new int[][] {
    {100, 90},
    {80},
    {70, 90, 100},
    {30, 90, 60},
    {40, 100}
};
 
System.out.println("번호\t평균"  );
System.out.println("=================");
for (int i = 0; i < score3.length; i++) {
    int sum2 = 0;
    double avg = 0.0;
 
    System.out.print((i+1) + "\t");
    for (int j = 0; j < score3[i].length; j++) {
        sum2 += score3[i][j];
    }
 
    avg = sum2/(double)score3[i].length;
    System.out.println(avg);
}

---

import java.util.*;
 
ArrayList list = new ArrayList();
list.add(1);
list.add("2");
list.add("abd");
list.add(4);
list.add(4, "다섯번째");
 
 
for (int i = 0; i < list.size(); i++) {
    System.out.println(list.get(i));
}
 
list.add("666");
 
for (int i = 0; i < list.size(); i++) {
    System.out.println(list.get(i));
}
 
 
HashMap map = new HashMap();
 
map.put(1, "일");
map.put(2222, "이");
map.put("삼", 33333);
map.put("weight", 107.4);
 
System.out.println(map.get(1));