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How to convert string representation of an ASCII value to character

I have a String containing ASCII representation of a character i.e.
String test = "0x07";
Is there a way I can somehow parse it to its character value.
I want something like
char c = 0x07;
But what the character exactly is, will be known only by reading the value in the string.

You have to add one step:
String test = "0x07";
int decimal = Integer.decode(test);
char c = (char) decimal;

A strange character

String str = "ิ";
System.out.println(str.length());
byte[] b = str.getBytes();
System.out.println(b[0]);
System.out.println(b[1]);
System.out.println(b[2]);
Above is my code.A speical char in str. It's length is one,but the byte is three.why? And how to make there become one? How to print this char use java code? And in my android phone this char can't delete.

Its because string is "encoded" into bytes, according to documentation
Encodes this String into a sequence of bytes using the platform's default charset, storing the
result into a new byte array.
The behavior of this method when this string cannot be encoded in the default charset is unspecified.
The CharsetEncoder class should be used when more control over the encoding process is required.

It seems like your special character is encoded using UTF-8. UTF-8 characters have different byte sizes, depending on their position in the range.
You can find the algorithm in the wikipedia page here and see how the size is determined.
From the Java String length() documentation:
The length is equal to the number of Unicode code units in the string.
Since the character is encoded using 3 bytes (whereas Unicode is one byte), you get a length of 3, rather than a length of 1 as you expect.

Lenght is NOT bytes
You have only 1 caracter, but this caracter is 3 bytes long. A String is made of several characters , but that doesnt mean that a 1 caracter string would be 1 byte.
About that caracter "ิ.
Java is by default using an UNICODE (encoding. "ิ is actually 0E34, this value beeing the THAI CHARACTER SARA.)
About your encoding issue
You need to change the way your application does its charset encoding and to use a utf-8 encoding instead.

Beside all the other comments. Here a small snippet to visualize it.
String str = "ิ"; // \u0E34
System.out.println("character length: " + str.length());
System.out.print("bytes: ");
for (byte b : str.getBytes("UTF-8")) {
System.out.append(Integer.toHexString(b & 0xFF).toUpperCase() + " ");
}
System.out.println("");
int codePoint = Character.codePointAt(str, 0);
System.out.println("unicode name of the codepoint: " + Character.getName(codePoint));
output
character length: 1
bytes: E0 B8 B4
unicode name of the codepoint: THAI CHARACTER SARA I

Java Char to its unicode hexadecimal string representation and vice-versa

I need to generate the hexadecimal code of Java characters into strings, and parse those strings again later. I found here that parsing can be performed as following:
char c = "\u041f".toCharArray()[0];
I was hoping for something more elegant like Integer.valueOf() for parsing.
How about generating the hexadecimal unicode properly?

This will generate a hex string representation of the char:
char ch = 'ö';
String hex = String.format("%04x", (int) ch);
And this will convert the hex string back into a char:
int hexToInt = Integer.parseInt(hex, 16);
char intToChar = (char)hexToInt;

After doing some deeper reading, the javadoc says the Character methods based on char parameters do not support all unicode values, but those taking code points (i.e., int) do.
Hence, I have been performing the following test:
int codePointCopyright = Integer.parseInt("00A9", 16);
System.out.println(Integer.toHexString(codePointCopyright));
System.out.println(Character.isValidCodePoint(codePointCopyright));
char[] toChars = Character.toChars(codePointCopyright);
System.out.println(toChars);
System.out.println();
int codePointAsian = Integer.parseInt("20011", 16);
System.out.println(Integer.toHexString(codePointAsian));
System.out.println(Character.isValidCodePoint(codePointAsian));
char[] toCharsAsian = Character.toChars(codePointAsian);
System.out.println(toCharsAsian);
and I am getting:
Therefore, I should not talk about char in my question, but rather about array of chars, since Unicode characters can be represented with more than one char. On the other side, an int covers it all.

On String level:
The following uses not char but int, say for Chinese, but is also adequate for chars.
int cp = "\u041f".codePointAt(0);
String s = new String(Character.toChars(cp));
On native2ascii level:
If you want to convert back and forth between \uXXXX and Unicode character, use from apache, commons-lang the StringEscapeUtils:
String t = StringEscapeUtils.escapeJava(s + "ö");
System.out.println(t);
On the command-line native2ascii can convert back and forth files between u-escaped and say UTF-8.

How to format numbers to a hex strings?

I want to format int numbers as hex strings. System.out.println(Integer.toHexString(1)); prints 1 but I want it as 0x00000001. How do I do that?

Try this
System.out.println(String.format("0x%08X", 1));

You can use the String.format to format an integer as a hex string.
System.out.println(String.format("0x%08X", 1));
That is, pad with zeros, and make the total width 8. The 1 is converted to hex for you. The above line gives: 0x00000001 and
System.out.println(String.format("0x%08X", 234));
gives: 0x000000EA

From formatting syntax documented on Java's Formatter class:
Integer intObject = Integer.valueOf(1);
String s = String.format("0x%08x", intObject);
System.out.println(s);

Less verbose:
System.out.printf("0x%08x", 1); //"Use %0X for upper case letters

I don't know Java too intimately, but there must be a way you can pad the output from the toHexString function with a '0' to a length of 8. If "0x" will always be at the beginning, just tack on that string to the beginning.

Java 17+
There is a new immutable class dedicated to conversion into and formatting hexadecimal numbers. The easiest way to go is using HexFormat::toHexDigits which includes leading zeroes:
String hex = "0x" + HexFormat.of().toHexDigits(1);
// 0x00000001
Beware, one has to concatenate with the "0x" prefix as such method ignores defined prefixes and suffixes, so the following snippet doesn't work as expected (only HexFormat::formatHex methods work with them):
String hex = HexFormat.of().withPrefix("0x").toHexDigits(1);
// 00000001
Returns the eight hexadecimal characters for the int value. Each nibble (4 bits) from most significant to least significant of the value is formatted as if by toLowHexDigit(nibble). The delimiter, prefix and suffix are not used.
Alternatively use the advantage of HexFormat::formatHex formatting to two hexadecimal characters, and a StringBuilder as an Appendable prefix containing "0x":
Each byte value is formatted as the prefix, two hexadecimal characters selected from uppercase or lowercase digits, and the suffix.
StringBuilder hex = HexFormat.of()
.formatHex(new StringBuilder("0x"), new byte[] {0, 0, 0, 1});
// 0x00000001
StringBuilder hex = HexFormat.of()
.formatHex(new StringBuilder("0x"), ByteBuffer.allocate(4).putInt(1).array());
// 0x00000001

You can use a java.util.Formatter or the printf method on a PrintStream.

This is String extension for Kotlin
//if lengthOfResultTextNeeded = 3 and input String is "AC", the result is = "0AC"
//if lengthOfResultTextNeeded = 4 and input String is "AC", the result is = "00AC"
fun String.unSignedHex(lengthOfResultTextNeeded: Int): String {
val count =
lengthOfResultTextNeeded - this.length
val buildHex4DigitString = StringBuilder()
var i = 1
while (i <= count) {
buildHex4DigitString.append("0")
++i
}
return buildHex4DigitString.toString() + this
}

Converting a string of text into alternate representations (binary, hex, ascii)

In Java, is there a simple method to convert the format of a given string? For example, I have the string "test22". I'd like the binary value and hex value. As well as possibly the ascii values of each character?

My solution would be to take the String, convert it to a char array, and then convert the integer values of the char array into binary or hex through the Integer.toBinaryString() or Integer.toHexString() or Integer.toOctalString() if you would like.
just replace binary string with hex and the function will do the same thing
public String convertToBinary(String str){
char [] array = str.toCharArray();
String binaryToBeReturned = "";
for(int i=0;i<str.length();i++){
binaryToBeReturned += Integer.toBinaryString((int)array[i]) + " ";
}
return binaryToBeReturned;
}
Also to get the ASCII values of the String int value = (int)string.charAt(i); will get the ASCII value.
I added a space just for formatting, not sure how you needed it formatted, and this is just a simple implementation.