Why doesn't regular expression work in Java?

Question

Java

Hello, I have this code:

String[] out_arr = out.split(" ");
for(int z=0; z < out_arr.length; z++){
if(out_arr[z].matches("[a-z]+")) {
System.out.println(out_arr[z]);
}

In out_arr in the debugger, you can see an array with something like this: "[" , "+", "342", "slovo1", "slovo", "*", "%"... etc. Those. there are values ​​in the array elements that fall under this regular expression, but it does not work. Why?