A teenager with a ''capacity for mindless violence'' while drunk has been sentenced to seven years' jail for stabbing three men in vicious, unprovoked attacks.

The crimes - two months apart - put one young man on an operating table with deep stomach injuries and left another fighting for his life with as many as 15 stab wounds.

The now-18-year-old Sudanese national, born in a Kenyan refugee camp, is set to stay behind bars until January 2015, by which time he'll be 20. He has spent 17 months on remand for the offences, committed when he was 16 and 17.

The teen, who cannot be named, accosted two victims at the Belconnen bus interchange in the early hours on April 2 last year.

The ACT Supreme Court on Thurs-day heard he stabbed one twice in the stomach and, when the other intervened, stabbed him in the arm.

The pair ran towards an underground car park with their assailant in pursuit.

One victim tried to take a photo on his phone, but dropped the device, which the assailant picked up. He then ran away when other people came into the area.

The first victim suffered deep stab wounds to his stomach, puncturing the lining and requiring surgery.

Hours earlier the same assailant threatened two youths at John Knight Memorial Park, holding a knife to one man's throat and striking the other with the flat of the blade.

Police arrested the youth, then aged 16, but released him on bail.

He told them he acted in self-defence at the bus stop, but later retreated from that claim.

The youth was still on bail on June 1 when involved in another incident, one Justice John Burns said was ''marked by a singular viciousness of execution''.

The youth and three others lured an 18-year-old to a Scullin flat on a Friday night under the pretence of drinking. They trapped him in a bedroom where the youth, armed with a flick knife, was waiting.

The Crown argued the boy stabbed the 18-year-old 15 times, although the defence maintained it was closer to seven, as two others watched and a fourth held the door shut.

''You inflicted grievous injury on [the victim], the physical consequences of which will be with him for the rest of his life, and the psychological consequences of which are likely to be with him for some time,'' Justice Burns said.

The badly injured and heavily bleeding man finally escaped and crossed the road to a supermarket, where he called for help before collapsing.

In a statement to the court the victim described it as the worst night of his life, and said he was lucky to be alive.

''The scars I have will never go away, I just want my confidence back,'' he said.

The accused eventually pleaded guilty to two counts of intentionally wounding, stealing a mobile phone and intentionally inflicting grievous bodily harm.

The judge also took into account two assault charges stemming from the Memorial Park incident.

The court heard the youth's upbringing in conflict-ravaged Africa was traumatic but did not leave him with post-traumatic stress disorder.

At the time of the first offence the youth had consumed about 20 standard drinks. The author of a pre-sentence report said he demonstrated ''a capacity for mindless violence when intoxicated''.

He was assessed as a moderate risk of offending again.

Justice Burns took the youth's age, lack of prior convictions, pleas of guilty, supportive family and positive life changes into account in his favour.

He imposed a seven-year sentence, backdated to June last year.

But the sentence will be suspended in January 2015 and the youth will enter a four-year good-behaviour order with conditions to steer clear of drugs and alcohol.