How to convert a char to a String?

Nice question. I've got of the following five 6 methods to do it.

// #1
String stringValueOf = String.valueOf('c'); // most efficient

// #2
String stringValueOfCharArray = String.valueOf(new char[]{x});

// #3
String characterToString = Character.toString('c');

// #4
String characterObjectToString = new Character('c').toString();

// #5
   // Although this method seems very simple, 
   // this is less efficient because the concatenation
   // expands to new StringBuilder().append(x).append("").toString();
String concatBlankString = 'c' + "";

// #6
String fromCharArray = new String(new char[]{x});

Note: Character.toString(char) returns String.valueOf(char). So effectively both are same.

String.valueOf(char[] value) invokes new String(char[] value), which in turn sets the value char array.

public String(char value[]) {
    this.value = Arrays.copyOf(value, value.length);
}

On the other hand String.valueOf(char value) invokes the following package private constructor.

String(char[] value, boolean share) {
    // assert share : "unshared not supported";
    this.value = value;
}

Source code from String.java in Java 8 source code

Hence String.valueOf(char) seems to be most efficient method, in terms of both memory and speed, for converting char to String.

1. How to convert primitive char to String in Java
2. How to convert Char to String in Java with Example

Below are various ways to convert to char c to String s (in decreasing order of speed and efficiency)

char c = 'a';
String s = String.valueOf(c);             // fastest + memory efficient
String s = Character.toString(c);
String s = new String(new char[]{c});
String s = String.valueOf(new char[]{c});
String s = new Character(c).toString();
String s = "" + c;                        // slowest + memory inefficient

Use the Character.toString() method like so:

char mChar = 'l';
String s = Character.toString(mChar);

Use any of the following:

String str = String.valueOf('c');
String str = Character.toString('c');
String str = 'c' + "";

As @WarFox stated - there are 6 methods to convert char to string. However, the fastest one would be via concatenation, despite answers above stating that it is String.valueOf. Here is benchmark that proves that:

@BenchmarkMode(Mode.Throughput)
@Fork(1)
@State(Scope.Thread)
@Warmup(iterations = 10, time = 1, batchSize = 1000, timeUnit = TimeUnit.SECONDS)
@Measurement(iterations = 10, time = 1, batchSize = 1000, timeUnit = TimeUnit.SECONDS)
public class CharToStringConversion {

    private char c = 'c';

    @Benchmark
    public String stringValueOf() {
        return String.valueOf(c);
    }

    @Benchmark
    public String stringValueOfCharArray() {
        return String.valueOf(new char[]{c});
    }

    @Benchmark
    public String characterToString() {
        return Character.toString(c);
    }

    @Benchmark
    public String characterObjectToString() {
        return new Character(c).toString();
    }

    @Benchmark
    public String concatBlankStringPre() {
        return c + "";
    }

    @Benchmark
    public String concatBlankStringPost() {
        return "" + c;
    }

    @Benchmark
    public String fromCharArray() {
        return new String(new char[]{c});
    }
}

And result:

Benchmark                                        Mode  Cnt       Score      Error  Units
CharToStringConversion.characterObjectToString  thrpt   10   82132.021 ± 6841.497  ops/s
CharToStringConversion.characterToString        thrpt   10  118232.069 ± 8242.847  ops/s
CharToStringConversion.concatBlankStringPost    thrpt   10  136960.733 ± 9779.938  ops/s
CharToStringConversion.concatBlankStringPre     thrpt   10  137244.446 ± 9113.373  ops/s
CharToStringConversion.fromCharArray            thrpt   10   85464.842 ± 3127.211  ops/s
CharToStringConversion.stringValueOf            thrpt   10  119281.976 ± 7053.832  ops/s
CharToStringConversion.stringValueOfCharArray   thrpt   10   86563.837 ± 6436.527  ops/s

As you can see, the fastest one would be c + "" or "" + c;

VM version: JDK 1.8.0_131, VM 25.131-b11

This performance difference is due to -XX:+OptimizeStringConcat optimization. You can read about it here.