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How to get value from List<> giving String as variable name [duplicate]

This question already has answers here:
Java: How can I access a class's field by a name stored in a variable?
(2 answers)
Closed 1 year ago.
I have a list based on database.
List<Contact> contactList;
There are many variables. For example:
String name;
String phone;
Can I get a specific value in way like this?
String var = "name";
String val = contactList.get(0).var <--- this Sting variable here
Is any way to do something like this? I don't want to write x10 :
if(var == "name"){
String val = contactList.get(0).name;
}
I think is way for do it, but I'm newbie, sorry if something is wrong with my question.
I will be very grateful for help.
Working code:
Thank you for answer. This is full code if someone will be looking for answer in the future:
private Map<String, Function<Contact, String>> map;
map = new HashMap<>();
map.put("Name", c -> c.name);
map.put("Phone", c -> c.phone);
map.put("Email", c -> c.email);
String some_val = map.get(second_value).apply(contactList.get(position));

You need a Map<String, Function<Contact, String>> containing method references, keyed by the property name.
For example:
// Construct this once, store in a static final field.
Map<String, Function<Contact, String> map =
Map.of("name", c -> c.name /* etc for other fields */);
// Then, when you want to get the value:
String val = map.get(var).apply(contactList.get(0));

Java: How to print the String value of a Map element? [duplicate]

This question already has answers here:
get string value from HashMap depending on key name
(10 answers)
Closed 3 years ago.
Could someone tell me how to get or print the String value of a map element?
The below code results in "The method values() is undefined for the type String."
I also tried .getValue() but the outcome is the same.
Thanks in advance!
Map<Integer, String> mapName = new HashMap<>();
mapName.put(0, "description_0");
mapName.put(1, "description_1");
for (Integer i : mapName.keySet()){
System.out.println(mapName.get(i).values());
}

Answer provided by #Lino.
for(String s : mapName.values()) System.out.println(s);

If you want to use stream:
mapName.entrySet().stream().forEach(elem-> System.out.println(elem));
This will allow you to use all the features of stream such as filtering,collecting , reducing etc.
https://www.geeksforgeeks.org/stream-map-java-examples/

Generate a Get query string in Java

I want to generate a Get query string in java like so
www.example.com/somethingToGet?key1=value&key2=value....
So my method has 2 parameters the base url(www.example.com/somethingToGet) is the first argument and the 2nd argument is a map data structure. I want to iterate over the map and generate a string like so
key1=value&key2=value....
It shouldn't end with ampersand.
I don't want to use any built in functions, I want to know the logic how such strings are generated.

Something like this:
public static String getQuery(String base, java.util.Map<String, String> map) {
StringBuilder str = new StringBuilder(base);
str.append('?');
boolean first = true;
for (java.util.Map.Entry<String, String> e : map.entrySet()) {
if (first)
first = false;
else
str.append('&');
str.append(e.getKey());
str.append('=');
str.append(e.getValue());
}
return str.toString();
}

You can also use the format method in URLEncoder class from the Apache HttpComponents library to create a query string. As per the documentation it
Returns a String that is suitable for use as an application/x-www-form-urlencoded list of parameters in an HTTP PUT or HTTP POST.

Good practice for method in java

I have a method that read from database and get some string there. According what I get I will override that string for another that I already know. For example:
str → string
bin → binary
and so on..
My question is, what is the best practice for doing this? Of course I already thought about if's...
if (str.equals("str"))
str = "string";
A file that have this things pre-defined, a multi-dimensional array, etc.. But this all seems a quite newbie, so what do you recommend? What is the best way?

Use a Map:
// create a map that maps abbreviated strings to their replacement text
Map<String, String> abbreviationMap = new HashMap<String, String>();
// populate the map with some values
abbreviationMap.put("str", "string");
abbreviationMap.put("bin", "binary");
abbreviationMap.put("txt", "text");
// get a string from the database and replace it with the value from the map
String fromDB = // get string from database
String fullText = abbreviationMap.get(fromDB);
You can read more about Maps here.

You could use a map, for example:
Map<String, String> map = new HashMap<String, String>();
map.put("str", "string");
map.put("bin", "binary");
// ...
String input = ...;
String output = map.get(input); // this could be null, if it doesn't exist in the map

Map is a good option as people have suggested. The other option which I normally consider in this scenario is Enum. It gives you an additional capability of adding behavior for a combination.

Can you reference a java variable from a string?

Hi I have a strange question about java. I will leave out the background info so as not to complicate it. If you have a variable named fname. And say you have a function returning a String that is "fname". Is there a way to say reference the identifier fname via the String "fname". The idea would be something like "fname".toIdentifier() = value but obviously toIdentifier isn't a real method.
I suppose a bit of background mite help. Basically I have a string "fname" mapped to another string "the value of fname". And I want a way to quickly say the variable fname = the value of the key "fname" from the map. I'm getting the key value pair from iterating over a map of cookies in the form . And I don't want to do "if key = "fname" set fname to "value of fname" because I have a ton of variables that need to be set that way. I'd rather do something like currentkey.toIdentifer = thevalue. Weird question maybe I'm overlooking a much easier way to approach this.

Why don't you just use a simple hashmap for this?
Map<String, String> mapping = new HashMap<String, String>();
mapping.put("fname", "someValue");
...
String value = mapping.get(key); //key could be "fname"

In a way you're describing what reflection is used for:
You refer to an object's fields and methods by name.
Java Reflection
However, most of the time when people ask a question like this, they're better off solving their problem by re-working their design and taking advantage of data structures like Maps.
Here's some code that shows how to create a Map from two arrays:
String[] keyArray = { "one", "two", "three" };
String[] valArray = { "foo", "bar", "bazzz" };
// create a new HashMap that maps Strings to Strings
Map<String, String> exampleMap = new HashMap<String, String>();
// create a map from the two arrays above
for (int i = 0; i < keyArray.length; i++) {
String theKey = keyArray[i];
String theVal = valArray[i];
exampleMap.put(theKey, theVal);
}
// print the contents of our new map
for (String loopKey : exampleMap.keySet()) {
String loopVal = exampleMap.get(loopKey);
System.out.println(loopKey + ": " + loopVal);
}
Here's a link to the JavaDoc for Map.