Dynamic variable names Java

Question

How will I be able to retrieve the value of a variable which has a dynamic name

For Example I have list of constants

public class Constant{
    public static final String S_R = "Standard(240)";
    public static final String S_W = "Standard(180)";
    public static final String L_R = "Large(360)";
    public static final String L_W = "Large(280)";
}

Based on database I build a variable name

String varName = "S" + "_"  +"R"; // This can be S_R , S_W , L_R or L_W
String varVal = // How do i get value of S_R

You can't do that and don't want to do that. You want a Map with "S_R", "S_W", ... as keys and the corresponding values. — Joachim Sauer
– Joachim Sauer, Commented Apr 27, 2011 at 14:40

Sanjay T. Sharma · Accepted Answer · 2011-04-27 14:40:03Z

11

Use a normal HashMap with variable names as strings against their values. Or use a EnumMap with enums as key and your value as values. AFAIK, that's the closest you can get when using Java. Sure, you can mess around with reflection but IMO the map approach is much more logical.

answered Apr 27, 2011 at 14:40

Sanjay T. Sharma

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Bozho · Accepted Answer · 2011-04-27 14:45:08Z

2

You can use a Map<String, String> and locate the value by its key.

Even better, you can have an enum:

public enum Foo {
    S_R("Standard", 240),
    S_W("Standard", 180),...;

    private String type;
    private String duration;

    // constructor and getters
}

And then call Foo.valueOf(name)

(You can also do this via reflection - Constants.class.getField(fieldName) and then call field.get(null) (null for static). But that's not really a good approach.)

edited Apr 27, 2011 at 14:45

answered Apr 27, 2011 at 14:40

Bozho

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3 Comments

Pit Digger Over a year ago

Using Enum Do you mean something like Constants.Foo.valueOf("S_R"); I tried that and didnt work. It returns "S_R"

Bozho Over a year ago

@user608576 get rid of Constants completely. Just Foo.valueOf("S_R"). It should return a Foo object on which you can call getType() and getDuration()

Joachim Sauer Over a year ago

@user608576: no, it does not return "S_R" (or at least not the String "S_R"). It returns the enum value S_R of which you'd get the type and/or duration using the appropriate getter methods, which you'd have to add).

Alnitak · Accepted Answer · 2011-04-27 14:40:22Z

1

If you really must do this (and it's unlikely), you would have to use the Java "reflection" APIs.

answered Apr 27, 2011 at 14:40

Alnitak

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