HashMap cityMap=new HashMap (；
.
for (ArrayList list : city map.values () ) )
int size=list.size (；
if(size0) {
list.removeif(I-true )；
}
}
id on ' tquiteunderstandwhattheremoveifdoesinthiscase.especiallythepart (I-true ).Thank you for any explanation。
解决方案
The Javadoc of removeIf () states:
removesalloftheelementsofthiscollectionthatsatisfythegivenpredicate。
thepredicateinyourexampleisalwaystruebecauseyoumapeachintegeriinyourlisttotruebytheexpression : I-true。
iaddedasimplerexamplewhichremovesallevenintegersandkeepsalloddintegersbythepredicatei %2==03:
Ugly setup:
List lists=new ArrayList () {}
add (new ArrayList (arrays.as list (1，2，3，4 ) )
add (new ArrayList (arrays.as list (2，4，6，8 ) )
add (new ArrayList (arrays.as list (1，3，5，7 ) )
}；
Keep only odd numbers:
列表列表3360列表(for ) {
list.removeif(I-I%2==0)；
}
Output:
[ 1，3 ]
[]
[ 1，3，5，7 ]