StringBuilder 作业

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#1 Created at ... [Delete] [Delete and Lock User]

static String buildInsertSql(String table, String[] fields) {

StringBuilder sb = new StringBuilder("INSERT INTO %s (%s) VALUES (%s)");

String[] insertStr = new String[]{table,String.join(", ", fields),String.join(", ", fields).replaceAll("\\w+", "?")};

int index = sb.indexOf("%s");

for(String str :insertStr){

sb.replace(index,index+2,str);

index = sb.indexOf("%s", index + 1);

}

return new String(sb);//sb.toString();

}

StringBuilder 相当于可变的String ，StringBuffer 除用于多线程同步以外和StringBuilder 没区别

#2 Created at ... [Delete] [Delete and Lock User]

StringBuilder 的默认容量为（16bytes + 初始化参数bytes）

如果其容量发生了溢出，则会双倍增幅当前容量 int newCapacity = (value.length + 1) * 2，并以此创建新容器

sb.capacity() 可用于查看当前容量

sb.length() 可用于查看当前有效字符长度

#3 Created at ... [Delete] [Delete and Lock User]

StringBuilder sb = new StringBuilder(64);

sb.append("INSERT INTO %s (%s) VALUES (%s)");

这样修改就不会发生溢出并重新创容器的过程