/**
 *  1) 字串字面量和常量稱為“靜態字串”<br>
 *  2) 字面量和常量的連線在編譯期間執行，優化為一個靜態字串<br>
 *  3) 在執行期間，Java在靜態緩衝池中建立靜態字串，並且儘量使用同一個字串物件。<br>
 *  4) 動態字串：字串運算結果，或者連線結果或者 new運算建立的字串，等執行期間建立的字串不參與靜態優化<br>
 * @author Heying
 *
 */

public static final String S = "123ABC";
public static final String SS = "ABC";
public static void main(String[] args) {
    String s1 = "123ABC";
    String s2 = 123 + SS;
    String s3 = 123 + "ABC";
    String s4 = 1+2+3+ "ABC";
    String s5 = "1"+2+3+ "ABC";
    String s6 = '1'+2+3+ "ABC";
    String s7 = "ABC";
    String s8 = 123+s7;
    String s9 = new String("123ABC");
    String s10 = "123abc".toUpperCase();

    System.out.println(s1); //123ABC
    System.out.println(s2); //123ABC
    System.out.println(s3); //123ABC
    System.out.println(s4); //6ABC
    System.out.println(s5); //123ABC
    System.out.println(s6); //54ABC
    System.out.println(s7); //ABC
    System.out.println(s8); //123ABC
    System.out.println(s9); //123ABC
    System.out.println(s10); //123ABC
}