Java 8, 57 bytes (94 bytes)

By the power of streams, my java answer shall be the shortest

Arrays.stream(a).max(Comparator.comparing(String::length))

Honestly I don't know if I cheated with that answer because I don't return anything but you could use that line of code. If we really want to return stuff then it's a bit longer.

String b(String[] a){return Arrays.stream(a).max(Comparator.comparing(String::length)).get();}

Java 8, 57 bytes (70 bytes)

By the power of streams, my java answer shall be the shortest

Arrays.stream(a).max(Comparator.comparing(String::length))

Honestly I don't know if I cheated with that answer because I don't return anything but you could use that line of code. If we really want to return stuff then it's a bit longer.

Thanks to LukeStevens for pointing out to use lambdas to be more golfy.

w->Arrays.stream(w).max(Comparator.comparing(String::length)‌​).get()

Java 8, 57 bytes (72 bytes)

By the power of streams, my java answer shall be the shortest

Arrays.stream(a).max(Comparator.comparing(String::length))

Honestly I don't know if I cheated with that answer because I don't return anything but you could use that line of code. If we really want to return stuff then it's a bit longer.

return Arrays.stream(a).max(Comparator.comparing(String::length)).get();

Java 8, 57 bytes (94 bytes)

By the power of streams, my java answer shall be the shortest

Arrays.stream(a).max(Comparator.comparing(String::length))

Honestly I don't know if I cheated with that answer because I don't return anything but you could use that line of code. If we really want to return stuff then it's a bit longer.

String b(String[] a){return Arrays.stream(a).max(Comparator.comparing(String::length)).get();}

JAVA 8, 57 bytes (72 bytes)

By the power of streams, my java answer shall be the shortest

Arrays.stream(a).max(Comparator.comparing(String::length))

Honestly I don't know if I cheated with that answer because I don't return anything but you could use that line of code. If we really want to return stuff then it's a bit longer.

return Arrays.stream(a).max(Comparator.comparing(String::length)).get();

Java 8, 57 bytes (72 bytes)

By the power of streams, my java answer shall be the shortest

Arrays.stream(a).max(Comparator.comparing(String::length))

Honestly I don't know if I cheated with that answer because I don't return anything but you could use that line of code. If we really want to return stuff then it's a bit longer.

return Arrays.stream(a).max(Comparator.comparing(String::length)).get();