Question: Daniel Johns and Justin Currie both did what in their respective music groups?

Context paragraphs:
What Is Love For: What is Love For is the first solo album by singer/songwriter Justin Currie, best known for his involvement in the band Del Amitri.

Del Amitri: Del Amitri is a Scottish alternative rock band, formed in Glasgow, Scotland in 1983.  The band grew out of Justin Currie's Jordanhill College School band and came together after a teenaged Currie placed an advertisement in the window of a music store asking for people who could play to contact him.  The band was formed with the original line-up of Currie (bass and vocals), Iain Harvie (lead guitar), Bryan Tolland (guitar) and Paul Tyagi (drums).  Currie and Harvie were the only members of the band to remain present throughout its history.  They were also the main songwriters of the group.

List of Afrikaans singers: This is a list of singers who have performed in the Afrikaans language.  Solo artists are alphabetised by their stage name or surname—whichever is more common.  Choirs that sing in Afrikaans are also included in the list, but other music groups are listed in the "Music groups" section below.

Justin Currie (American football): Justin Currie (born September 19, 1993) is an American football safety who is currently a free agent.  He played college football at Western Michigan and was signed by the New York Giants as an undrafted free agent in 2015.

The Great War (album): The Great War is the second solo album by singer/songwriter Justin Currie, best known for his involvement in the band Del Amitri.

Iain Harvie: Iain Wallace Harvie (born 19 May 1962 in Glasgow, Scotland) is the guitarist with the Scottish rock band Del Amitri.  Along with lead singer and bassist Justin Currie, Harvie is one of only two members to be present throughout Del Amitri's history since its 1982 inception.  He is also the co-writer, with Currie, of many of the group's songs.

Daniel Johns: Daniel Paul Johns (born 22 April 1979) is an Australian musician, singer, and songwriter.  Best known as the former front man of the rock band Silverchair, Johns is also one half of The Dissociatives with Paul Mac and, in 2007, was ranked at number 18 on "Rolling Stone"' s list of The 25 Most Under-rated Guitarists.

Justin Currie: Justin Robert Currie (born 11 December 1964) is a Scottish singer and songwriter, best known as a founding member of the band Del Amitri and, along with Iain Harvie, is one of only two members of the group to be present throughout its entire existence.

Lower Reaches: Lower Reaches is the third solo album by singer/songwriter Justin Currie, best known for his involvement in the band Del Amitri.

Diorama (Silverchair album): Diorama is the fourth studio album by Australian alternative rock band Silverchair.  Released on 31 March 2002 by Atlantic/.  It won the 2002 ARIA Music Award for Best Group and Best Rock Album.  The album was co-produced by Daniel Johns and David Bottrill.  While Bottrill had worked on albums for a variety of other bands, "Diorama" marked the first production credit for lead singer Johns.

Supporting paragraphs: Daniel Johns Justin Currie
Answer: singer and songwriter