New to Java

Hi, i'm new to java.
I have to find out what trails are.
so i found some lines like that:

public void setAmount(String amount)
{
this.amount = amount;
}

@Id(generate=GeneratorType.AUTO)
public Integer getId()
{
return id;
}

public void setId(Integer id)
{

as you can see, there's a litte "@" at the beginning of the sixths line.
can anyone imagine what's the meaning of this symbol(whole line)?