concatenation

问题 As far as i know + operator in Java String is overloaded and while we are using + operator it automatically chooses StringBuffer or StringBuilder to concatenate strings with better performance. Only exception of this is while we are using + operator inside a loop. In this case Java doesn't use benefits of StringBuffer and StringBuilder. Is that true? I will concatenate 40 Strings (around 4500 chars) and I will repeat it so often so I wanted be sure about it. 回答1: No, Java will always (almost

问题 I have <a href> tag in html My model has a java list list1 as model attribute. I am trying to construct <a href="pathvalue/namevalue"> <c:forEach var="obj" items="${list}"> <a href="${obj.path}+"/"+${obj.name}".../> </c:forEach> I want to know how can I insert "/". I can directly concate two El value ${obj.path}${obj.name} but how to get that "/" is below line correct to get a output "pathvalue/namevalue"? <c:out value="${obj.path+'/'+obj.name}" /> 回答1: You can't concatenate it because "+"

问题 I have a table of products with their owners. Each owner is in their own row and has an owner type of either primary or secondary. Not every product has a secondary owner. I need to get a table grouped by product with the primary owner in one column and all the secondary owners concatenated in a second column. If a product has multiple primary owners it should select the first one and the rest go to the secondary owners. If a product doesn't have a primary owner then it should just select the

问题 I have matlab files with an integer in each name of my variables inside (except the first one). I want to loop to concatenate the name of the integers. There is my code: library('R.matlab') mat <- readMat('SeriesContPJM.mat') #str(mat) #typeof(mat) #mat[[1]] write.csv(mat$vol.PJM$data[[4]][[1]], "PJM.csv") i = 2 while (i < 7) { write.csv(get(paste("mat$vol.PJM", as.character(i), "$data[[4]][[1]]", sep = "")), paste(paste("PJM", as.character(i), sep="_"), "csv", sep =".")) i = i + 1 } I have

问题 This question already has answers here : Comparing strings with == which are declared final in Java (6 answers) a confusion about java String literal pool and String's concatenation (4 answers) Closed 5 years ago . When I write the following code int a = "Java"; the java compiler displays the following error : cannot convert from String to int So the constant Java is considered as an object derived from String class. - Is it true that each list of characters contained between "" is considered

问题 What is the correct way to concatenate a variable when using the oledb command function in c# for a sql query. To apply some context im trying to make what a list box displays dependent on another selection made on a previous list box.This is what I've tried but doesn't work. OleDbCommand projects = new OleDbCommand("SELECT * FROM Client_projects WHERE clients = " + (listBox1.SelectedItem.ToString()) , conn); OleDbDataReader project = projects.ExecuteReader(); while (project.Read()) { // Add

问题 I have 367 .txt files that I need to concatenate into one big .txt file through the windows cmd prompt. Each file has the name and date on it, e.g., andx.20150401.000000.txt, andx.20150402.000000.txt, ..., andx.20160401.000000.txt Inside each file I have 7 columns for time (in julians) and 6 other measurable variables. I need a continuous file for all 367 and I wanted to do this through the cmd prompt. 回答1: I suppose you could do this as one command if the directory is clear of old files that

问题 I am trying to merge & append different timeseries, importing them from csv files. I have tried the following basic code: import pandas as pd import numpy as np import glob import csv import os path = r'./A08_csv' # use your path #all_files = glob.glob(os.path.join(path, "A08_B1_T5.csv")) df5 = pd.read_csv('./A08_csv/A08_B1_T5.csv', parse_dates={'Date Time'}) df6 = pd.read_csv('./A08_csv/A08_B1_T6.csv', parse_dates={'Date Time'}) print len(df5) print len(df6) df = pd.concat([df5],[df6], join=

问题 I have a select2 search form with an ajaxform that concatenates new form entries into the original select2 search form. If more than one new entry is added, the new text values concatenate correctly into the search field, however, any new hidden ID replaces the existing one. It appears to be added because all new text values shows in the select2 search field. I think the issue is that the new ID should be concatenating to the hidden cropstageid field in addition to the text field

问题 I have the following table. Animal Vaccine_Date Vaccine Cat 2/1/2016 y Cat 2/1/2016 z Dog 2/1/2016 z Dog 1/1/2016 x Dog 2/1/2016 y I would like to get the results to be as shown below. Animal Vaccine_Date Vaccine Dog 1/1/2016 x Dog 2/1/2016 y,z Cat 2/1/2016 y,z I have the following code which was supplied via my other post at "Combine(concatenate) rows based on dates via SQL" WITH RECURSIVE recCTE AS ( SELECT animal, vaccine_date, CAST(min(vaccine) as VARCHAR(50)) as vaccine, --big enough to