There are answers that address what OP should do to improve but I feel the important part in his question my arraylist cannot resolved. is not discussed. My answer adds to that part.
When compilers complain XXX cannot be resolved, it means that the compiler is encountering the variable's name for the first time and has no idea of what the stuff with that name is. In your case, the compiler does not know what is Strings in showFirstString(), and because it does not know what is Strings, it stops compiling and complains to you instead of keep going with knowing nothing about it, which could potentially be dangerous.
The reason the compiler could not know what was Strings in showFirstString() is known as the scope of variables. Basically, there are lots of blocks in Java as in:
public void myMethod()
{ /* method body block is here* }
or even like,
public class myClass
{
/* here starts the class body */
public static void myMethod()
{ /* method body block is here* }
}
And the thing is that the variables are known only within a block where it's declared. So for example, if your codes looks like this:
public class myClass
{
int foo; // it is known to everywhere within this class block
public static void myMethod()
{
// boo is known only within this method
int boo = foo + 1; // fine, it knows what foo is
}
public static void myMethod2()
{
// bar is known only within this method
int bar = boo + 1; // cause errors: it does not know what boo is
}
}
Now you should understand why your programme was not able to know what is Strings. But passing around data within your codes is a common stuff that is often required to do. To achieve this, we pass parameters to methods. A parameter is a data specified within () that follows the name of the method.
For example:
public class myClass
{
int foo; // it is known to everywhere within this class block
public static void myMethod()
{
// boo is known only within this method
int boo = foo + 1; // fine, it knows what foo is
myMethod2(boo); // value of boo is passed to myMethod2
}
public static void myMethod2(int k) // value of k will be boo
{
// bar is known only within this method
int bar = k + 1; // cause errors: it does not know what boo is
}
}
With parameters like above, you can use boo in myMethod2(). The final thing is that with the codes above, your codes will compile but will do nothing when you run it, because you did not start any of the methods. When a programme runs, it looks for the main method and any other methods that you want to invoke should be called in methods, or by other methods that are in main.
public class myClass
{
int foo; // it is known to everywhere within this class block
public static void main(String[] args)
{
// start myMethod
myMethod();
}
public static void myMethod()
{
// boo is known only within this method
int boo = foo + 1; // fine, it knows what foo is
myMethod2(boo); // value of boo is passed to myMethod2
}
public static void myMethod2(int k) // value of k will be boo
{
// bar is known only within this method
int bar = k + 1; // cause errors: it does not know what boo is
}
}
I hope you get the idea. Also note that to get the items in an ArrayList, you need to use ArrayList.get(int index), as others noted.
