Helper (devpack 3.6.1 API)

java.lang.Object
- io.neow3j.devpack.Helper

```
public class Helper
extends java.lang.Object
```
Provides helper methods to be used in a smart contract.

Constructor Summary

Constructors
Constructor and Description

Helper()

Constructors
Constructor and Description
`Helper()`

Method Summary

All Methods Static Methods Concrete Methods
Modifier and Type	Method and Description
`static void`	`abort()` Aborts the execution of the contract.
`static byte`	`asByte(int value)` Asserts that the given value is in the range [-128, 127], i.e., the value range of a signed byte.
`static void`	`assertTrue(boolean condition)` Asserts if the given boolean is true.
`static byte`	`asSignedByte(int value)` Asserts that the given value is in the range [0, 255], i.e., the range of an unsigned byte.
`static byte[]`	`concat(byte[] first, byte[] second)` Concatenates the two given byte arrays.
`static java.lang.String`	`concat(java.lang.String first, java.lang.String second)` Concatenates the two given strings.
`static byte[]`	`last(byte[] source, int n)` Returns the last n elements of the given byte array.
`static java.lang.String`	`last(java.lang.String source, int n)` Returns the last n characters of the given String.
`static byte[]`	`range(byte[] source, int index, int n)` Returns n consecutive bytes from the given source starting at the given index.
`static java.lang.String`	`range(java.lang.String source, int index, int n)` Returns n consecutive characters from the given string starting at the given index.
`static byte[]`	`reverse(byte[] source)` Returns a reversed copy of the given bytes.
`static java.lang.String`	`reverse(java.lang.String source)` Returns a reversed copy of the given string.
`static byte[]`	`take(byte[] source, int n)` Returns the first n elements from the given byte array.
`static java.lang.String`	`take(java.lang.String source, int n)` Returns the first n characters from the given string.
`static byte[]`	`toByteArray(byte source)` Converts the given byte to a byte array.
`static byte[]`	`toByteArray(java.lang.String source)` Converts the given string to a byte array using UTF-8 encoding.
`static java.lang.String`	`toByteString(byte[] source)` Casts the given byte array to a string.
`static int`	`toInt(byte[] source)` Converts the given byte array to an integer.
`static boolean`	`within(int x, int a, int b)` Checks if the value of x is in the range [a, b).

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - Helper
```
public Helper()
```
- Method Detail
  - assertTrue
```
public static void assertTrue(boolean condition)
```
    Asserts if the given boolean is true. If not, makes the smart contract exit in a fault state. Otherwise, execution continues normally.
    
    Parameters:
    
    condition - The condition to check.
  - abort
```
public static void abort()
```
    Aborts the execution of the contract.
  - toByteArray
```
public static byte[] toByteArray(byte source)
```
    Converts the given byte to a byte array.
    
    Parameters:
    
    source - The byte to convert.
    
    Returns:
    
    the converted byte array.
  - toByteArray
```
public static byte[] toByteArray(java.lang.String source)
```
    Converts the given string to a byte array using UTF-8 encoding.
    This method cannot be used to convert a Neo address to a valid script hash byte array, or a script hash in hexadecimal format into its corresponding byte array.
    Examples
    - "hello": [0x68656c6c6f]
    - "": []
    - "Neo": [0x4e656f]
    Parameters:
    
    source - The string to convert.
    
    Returns:
    
    the converted byte array.
  - asByte
```
public static byte asByte(int value)
```
    Asserts that the given value is in the range [-128, 127], i.e., the value range of a signed byte. Returns the value as a signed byte if true, faults if not.
    Examples:
    - 255: fault
    - -128: [0x80]
    - 0: [0x00]
    - 10: [0x0a]
    - 127: [0x7f]
    Parameters:
    
    value - The value to cast.
    
    Returns:
    
    the casted byte.
  - asSignedByte
```
public static byte asSignedByte(int value)
```
    Asserts that the given value is in the range [0, 255], i.e., the range of an unsigned byte. Returns the value as a signed byte if true, faults if not.
    - 256: fault
    - -1: fault
    - 255: -1 [0xff]
    - 0: 0 [0x00]
    - 10: 10 [0x0a]
    - 127: 127 [0x7f]
    - 128: -128 [0x80]
    Parameters:
    
    value - The value to cast.
    
    Returns:
    
    the casted byte.
  - toInt
```
public static int toInt(byte[] source)
```
    Converts the given byte array to an integer. The byte array is assumed to be a two's complement in little-endian format.
    The value of the converted integer can be outside of Integer.MAX_VALUE because the neo-vm doesn't have that limit for int as the JVM has.
    Examples
    - [0x0a]: 10
    - [0x80]: -128
    - [0xff80]: -32513
    - []: 0
    - [0xff00]: 255
    - [0xfba600]: 42747
    Parameters:
    
    source - The byte array to convert.
    
    Returns:
    
    the converted integer.
  - toByteString
```
public static java.lang.String toByteString(byte[] source)
```
    Casts the given byte array to a string. Assumes that the byte array is a UTF-8 encoded string.
    In the NeoVM strings are represented as ByteStrings. Hence the method name.
    Examples:
    - [0x68656c6c6f]: "hello"
    - []: ""
    - [0x4e656f]: "Neo"
    Parameters:
    
    source - The byte array to cast.
    
    Returns:
    
    the string.
  - within
```
public static boolean within(int x,
                             int a,
                             int b)
```
    Checks if the value of x is in the range [a, b).
    Examples: x=5 a=5 b=15 is true; x=15 a=5 b=15 is false
    
    Parameters:
    
    x - The value to check if it is in the range.
    
    a - The beginning of the range (inclusive).
    
    b - The end of the range (exclusive).
    
    Returns:
    
    true iff a <= x < b. False, otherwise.
  - concat
```
public static byte[] concat(byte[] first,
                            byte[] second)
```
    Concatenates the two given byte arrays.
    
    Parameters:
    
    first - The first byte array.
    
    second - The second byte array.
    
    Returns:
    
    the concatenation.
  - concat
```
public static java.lang.String concat(java.lang.String first,
                                      java.lang.String second)
```
    Concatenates the two given strings.
    
    Parameters:
    
    first - The first string.
    
    second - The second string.
    
    Returns:
    
    the concatenation.
  - range
```
public static java.lang.String range(java.lang.String source,
                                     int index,
                                     int n)
```
    Returns n consecutive characters from the given string starting at the given index.
    
    Parameters:
    
    source - The string to take the bytes from.
    
    index - The start index of the range (inclusive).
    
    n - The size of the range, i.e. number of characters to take.
    
    Returns:
    
    the defined range of the given string.
  - range
```
public static byte[] range(byte[] source,
                           int index,
                           int n)
```
    Returns n consecutive bytes from the given source starting at the given index.
    
    Parameters:
    
    source - The array to take the bytes from.
    
    index - The start index of the range (inclusive).
    
    n - The size of the range, i.e. number of bytes to take.
    
    Returns:
    
    the defined range of the given byte array.
  - take
```
public static byte[] take(byte[] source,
                          int n)
```
    Returns the first n elements from the given byte array. Faults if n < 0.
    
    Parameters:
    
    source - The array to take the bytes from.
    
    n - The number of bytes to return.
    
    Returns:
    
    the first n bytes.
  - take
```
public static java.lang.String take(java.lang.String source,
                                    int n)
```
    Returns the first n characters from the given string. Faults if n < 0.
    
    Parameters:
    
    source - The string to take the characters from.
    
    n - The number of characters to return.
    
    Returns:
    
    the first n characters.
  - last
```
public static byte[] last(byte[] source,
                          int n)
```
    Returns the last n elements of the given byte array. Faults if n < 0.
    
    Parameters:
    
    source - The array to take the bytes from.
    
    n - The number of bytes to return.
    
    Returns:
    
    the last n bytes.
  - last
```
public static java.lang.String last(java.lang.String source,
                                    int n)
```
    Returns the last n characters of the given String. Faults if n < 0.
    
    Parameters:
    
    source - The string.
    
    n - The number characters to return.
    
    Returns:
    
    the last n characters.
  - reverse
```
public static byte[] reverse(byte[] source)
```
    Returns a reversed copy of the given bytes. Example: [0a,0b,0c,0d,0e]: [0e,0d,0c,0b,0a]
    
    Parameters:
    
    source - The bytes to reverse.
    
    Returns:
    
    The reversed bytes.
  - reverse
```
public static java.lang.String reverse(java.lang.String source)
```
    Returns a reversed copy of the given string.
    
    Parameters:
    
    source - The string to reverse.
    
    Returns:
    
    The reversed string.

Class Helper

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

Helper

Method Detail

assertTrue

abort

toByteArray

toByteArray

asByte

asSignedByte

toInt

toByteString

within

concat

concat

range

range

take

take

last

last

reverse

reverse