A defence force dropout has been jailed for kicking a young woman in the face, stealing her violin and electric tuner and stabbing her friend in the back.

Key points: Convicted criminal Jeremy Cooper was already on a suspended sentence for choking a three-year-old

Convicted criminal Jeremy Cooper was already on a suspended sentence for choking a three-year-old Justice Anthony Graham has described the attack as "senseless and foolish"

Justice Anthony Graham has described the attack as "senseless and foolish" Cooper was sentenced to jail for two counts, and had his previous suspended sentence restored

Hooded in a balaclava and dressed in dark clothing, Jeremy Cooper, 23, attacked his two young, random victims who were "harmlessly enjoying the evening" on Darwin CBD's scenic Esplanade on June 30, 2018, the NT Supreme Court heard.

At 7:20pm that night, Cooper approached the woman, who the ABC has chosen not to name, and demanded she hand over "everything".

"She handed the offender her wallet and he took out the contents, which were $10 in Australian and Indonesian currency," the court heard.

"He then threw the wallet back to the female victim.

"He then grabbed her violin case which contained her violin and electric tuner."

When the woman's friend tried to intervene, Cooper stabbed him in the middle of his back.

"The offender [then] once again grabbed the violin case," the court heard.

"The female victim pleaded with the offender to leave the violin with her. He told her to shut up twice before kicking her in the face."

Offender was wearing electronic monitor

Acting Justice Anthony Graham branded the attack as "horrific" and "simply stupid" for the fact Cooper was already wearing an electronic monitoring device when he committed the violent act.

"Upon checking this device, it was confirmed by the police that he had been at The Esplanade at the time of the offending," Acting Justice Graham said.

Police found Cooper in the hostel where he lived with the violin still in his possession.

"It was senseless and foolish ... the offender was bound to be apprehended."

Cooper, who completed a defence force infantry course but dropped out in 2015 due to the army being "too stressful", was in the middle of a suspended sentence for "holding a [three-year-old] child's throat in a chokehold, causing her to be starved of oxygen, aspirate and have a seizure" when he committed the Esplanade crime.

Following the attack, the woman was left bruised and shaken and the young man with a two-centimetre stab wound, from which it took him five months to recover.

Cooper was sentenced to four years and three months in jail, which included the restoration of his suspended sentence, backdated to June last year.