java String

public static void main(String[] args) {String str1 = "aaa";    String str2 = "aaa";    String str3 = new String("aaa");    String str4 = str1+"";    String str5 = "aa"+"a";    System.out.println(str1 == str3);    System.out.println(str1.equals(str3));    System.out.println(str1==str2);    System.out.println(str1 == str4);    System.out.println(str3 == str4);    System.out.println(str1 == str5);/** * String 相加 ==> str4 = str1+"";     *//*    String str1 = "aaa";    StringBuilder sb = new StringBuilder();    sb.append(str1).append("");    String str4 = sb.toString();*/}

结果：

false

true

true

false

false

true

所以有大量“+”的拼接操作时用StringBuilder或者StringBuffer会省下很多内存;

StringBuilder和StringBuffer作用类似,只是StringBuffer的由于增加了同步锁是线程安全的，但是会稍微影响性能;