# Prompt Template Class

The `PromptTemplate` class is part of the `ai.knowly.langtoch.prompt.template` package. It represents a string template with variables that can be replaced with specified values. The template uses the format `{{$var}}` for variables, where variables must be one or more word characters (letters, digits, or underscores).

### Usage

To create an instance of the `PromptTemplate`, use the `builder()` method to create a new `Builder` object. Use the builder's methods to set the template, examples, example header, and variables as needed, then call `build()` to create the `PromptTemplate`.

```java
PromptTemplate promptTemplate = PromptTemplate.builder()
    .setTemplate("Hello, {{$name}}!")
    .addVariableValuePair("name", "John")
    .build();
```

### Public Methods

#### format()

The `format()` method replaces the variables in the template with their corresponding values and returns the formatted string. If an optional example header and examples are provided, they are included in the formatted string.

```java
String formattedTemplate = promptTemplate.format(); // "Hello, John!"
```

### Builder

The `Builder` class is an inner class of `PromptTemplate`. It is used to create instances of the `PromptTemplate` class. The following methods are available:

#### setTemplate(String template)

Sets the template string containing variables in the form of `{{$var}}`.

#### setExamples(List\<String> examples)

Sets a list of strings to be used as examples for few-shot prompting.

#### setExampleHeader(String exampleHeader)

Sets an optional string that can be used to describe the examples.

#### addVariableValuePair(String variableName, String value)

Adds a variable name-value pair to the variables map.

#### addAllVariableValuePairs(Map\<String, String> variables)

Adds all variable name-value pairs from the provided map to the variables map.

#### build()

Creates and returns a new instance of the `PromptTemplate` class with the specified values.