total+=getArea（x[0],y[0],x[i],y[i],x[i+1],y[i+1]）;
}
System.out.println（"Thetotalareais"+total）;
}
publicstaticdoublegetArea（doublex1,doubley1,doublex2,doubley2,doublex3,doubley3）{
doubles1=Math.sqrt（（x1-x2）*（x1-x2）+（y1-y2）*（y1-y2））;
doubles2=Math.sqrt（（x1-x3）*（x1-x3）+（y1-y3）*（y1-y3））;
doubles3=Math.sqrt（（x3-x2）*（x3-x2）+（y3-y2）*（y3-y2））;
doubles=（s1+s2+s3）/2;
returnMath.sqrt（s*（s-s1）*（s-s2）*（s-s3））;
}
}
7.3
publicclassExercise07_03{
publicstaticvoidmain（String[]args）{
Scannerinput=newScanner（System.in）;
int[]counts=newint[100];
System.out.print（"Entertheintegersbetween1and100:
"）;
//Readallnumbers
intnumber=input.nextInt（）;//numberreadfromafile
while（number!
=0）{
if（number<=100&&number>=0）
counts[number-1]++;
number=input.nextInt（）;
}
//Displayresult
for（inti=0;i<100;i++）{
if（counts[i]>0）
System.out.println（（i+1）+"occurs"+counts[i]
+（（counts[i]==1）?
"time":
"times"））;
}
}
}
7.3附加
publicclassExercise07_03Extra{
publicstaticvoidmain（String[]args）{
intcount=0;//Howmanysolutionsarefound?
//Queenpositions
int[]queens=newint[8];//queensareplacedat（i,queens[i]）
for（inti=0;i<8;i++）
queens[i]=-1;//-1indicatesthatnoqueeniscurrentlyplacedinthe
//ithrow
queens[0]=0;//Initially,placeaqueenat（0,0）inthe0throw
//k-1indicatesthenumberofqueensplacedsofar
//Wearelookingforapositioninthekthrowtoplaceaqueen
intk=1;
while（k>=0）{
//Findapositiontoplaceaqueeninthekthrow
intj=findPosition（k,queens）;
if（j<0）{
queens[k]=-1;
k--;//backtracktothepreviousrow
}else{
queens[k]=j;
if（k==7）{
count++;//Onemoresolutionfound
System.out.println（"Solution"+count+":
"）;
printResult（queens）;
}else{
k++;
}
}
}
System.out.println（"Howmanysolutions?
"+count）;
}
publicstaticintfindPosition（intk,int[]queens）{
intstart=queens[k]==-1?
0:
queens[k]+1;
for（intj=start;j<8;j++）{
if（isValid（k,j,queens））
returnj;//（k,j）istheplacetoputthequeennow
}
return-1;
}
/**Returntrueifyouaqueencanbeplacedat（k,j）*/
publicstaticbooleanisValid（intk,intj,intqueens[]）{
//Seeif（k,j）isapossibleposition
//Checkjthcolumn
for（inti=0;iif（queens[i]==j）
returnfalse;
//Checkmajordiagonal
for（introw=k-1,column=j-1;row>=0&&column>=0;row--,column--）
if（queens[row]==column）
returnfalse;
//Checkminordiagonal
for（introw=k-1,column=j+1;row>=0&&column<=7;row--,column++）
if（queens[row]==column）
returnfalse;
returntrue;
}
/**Printatwo-dimensionalboardtodisplaythequeens*/
publicstaticvoidprintResult（int[]queens）{
//Displaytheoutput
for（inti=0;i<8;i++）{
for（intj=0;jSystem.out.print（"|"）;
System.out.print（"|Q|"）;
for（intj=queens[i]+1;j<8;j++）
System.out.print（"|"）;
System.out.println（）;
}
}
}
7.4
publicclassExercise07_04{
//Mainmethod
publicstaticvoidmain（String[]args）{
double[]scores=newdouble[100];
doublesum=0;
intcount=0;
doubleitem;
java.util.Scannerinput=newjava.util.Scanner（System.in）;
do{
System.out.print（"Enteranewscore:
"）;
item=input.nextDouble（）;
if（item>=0）{
scores[count]=item;
sum+=item;
count++;
}
}while（item>=0）;
System.out.println（"countis"+count）;
doubleaverage=（sum）/count;
intnumOfAbove=0;
intnumOfBelow=0;
for（inti=0;iif（scores[i]>=average）{
numOfAbove++;
}else{
numOfBelow++;
}
}
System.out.println（"Averageis"+average）;
System.out.println（"Numberofscoresaboveorequaltotheaverage"
+numOfAbove）;
System.out.println（"Numberofscoresbelowtheaverage"+numOfBelow）;
}
}
7.4附加
publicclassExercise07_04Extra{
publicstaticvoidmain（String[]args）{
//Prompttheusertoenterastring
java.util.Scannerinput=newjava.util.Scanner（System.in）;
System.out.print（"Enterastring:
"）;
Strings=input.nextLine（）;
int[]counts=count（s）;
for（inti=0;i<10;i++）{
System.out.println（"Digit"+i+"occurs"+counts[i]+
"times"）;
}
}
publicstaticint[]count（Strings）{
int[]counts=newint[10];
for（inti=0;iif（Character.isDigit（s.charAt（i）））{
counts[s.charAt（i）-'0']++;
}
}
returncounts;
}
}
7.5
/*
方法:
useanarraynumberstostorethedistinctvalues.
readeachvaluefrominput,checkifitisalreadyinthearraynumbers,
ifnot,additintoit.
//Suggestedtemplate:
publicclassExercise07_05{
publicstaticvoidmain（String[]args）{
//numbersarraywillstoredistinctvalues,maximumis10
int[]numbers=newint[10];
//Howmanydistinctnumbersareinthearray
intnumberOfDistinctValues=0;
java.util.Scannerinput=newjava.util.Scanner（System.in）;
System.out.print（"Entertennumbers:
"）;
for（inti=0;i//Readaninput
intvalue=input.nextInt（）;
步骤1:
Checkifvalueisinnumbers
步骤2:
Ifvalueisnotinnumbers,additintonumbers
步骤3:
IncrementnumberOfDistinctValues
}
步骤4:
Displayoutput
}
}
解法1：
publicclassExercise07_05{
publicstaticvoidmain（String[]args）{
int[]numbers=newint[30];//numbersarraywillstoredistinctvalues,maximumis10
intnumberOfDistinctValues=0;//Howmanydistinctnumbersareinthe
//array
java.util.Scannerinput=newjava.util.Scanner（System.in）;
System.out.print（"Enter"+numbers.length+"numbers:
"）;
for（inti=0;i//Readaninput
intvalue=input.nextInt（）;
//Step1:
Checkifvalueisinnumbers
booleanisInTheArray=false;
for（intj=0;jif（value==numbers[j]）{
isInTheArray=true;
}
}
//Step2:
Ifvalueisnotinnumbers,additintonumbers
if（!
isInTheArray）{
numbers[numberOfDistinctValues]=value;
//Step3:
IncrementnumberOfDistinctValues
numberOfDistinctValues++;
}
}
System.out.println（"Thenumberofdistinctvaluesis"
+numberOfDistinctValues）;
for（inti=0;iSystem.out.print（numbers[i]+""）;
}
}
解法2：
publicclassExercise07_05{
publicstaticvoidmain（String[]args）{
int[]numbers=newint[30];//numbersarraywillstoredistinctvalues,maximumis10
intnumberOfDistinctValues=0;//Howmanydistinctnumbersareinthe
//array
java.util.Scannerinput=newjava.util.Scanner（System.in）;
System.out.print（"Enter"+numbers.length+"numbers:
"）;
for（inti=0;i//Readaninput
intvalue=input.nextInt（）;
//Step1:
Checkifvalueisinnumbers
booleanisInTheArray=false;
fo
升级会员 