String formatting with variable number of arguments in java

Question

Consider a string.

String Str = "Entered number = %d and string = %s"

Let us say I have a list of objects

List<Objects> args = new ArrayList<Objects>();
args.add(1);
args.add("abcd");

Is there any way in which I can substitute these args into Str , so that i get a string like "Entered number = 1 and string = abcd " ?

By generalizing this I was planning to dump all the questions and arguments in a file (like json) and execute them at run time. Please do let me know if there are better ways to do this.

Solution 1

Try:

String formatted = String.format(str, args.toArray());

This gives:

Entered number = 1 and string = abcd

Solution 2

You can use the following:

String str = "Entered number = %d and string = %s";

List<Object> args = new ArrayList<Object>();
args.add(1);
args.add("abcd");

System.out.println(String.format(str, args.toArray()));

will give the output:

Entered number = 1 and string = abcd

From JLS 8.4.1 Format parameters:

The last formal parameter in a list is special; 
it may be a variable arity parameter, indicated by an 
elipsis following the type.

If the last formal parameter is a variable arity parameter of type T, 
it is considered to define a formal parameter of type T[]. 
The method is then a variable arity method. Otherwise, it is a fixed arity 
method. Invocations of a variable arity method may contain more actual 
argument expressions than formal parameters. All the actual argument 
expressions that do not correspond to the formal parameters preceding 
the variable arity parameter will be evaluated and the results stored 
into an array that will be passed to the method invocation.

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Comments

[Zohaib]

str.replaceAll("%d", (String)args.get(1));