1.申明

int [][] array1 ={  {1,2,3} , {0} , {2,2,2,2,2} , {5,6} };  锯齿数组

int [][] array2 = new int [5][ ];    // new int[5][] 创建数组时，必须指定第一个下标标。语法new int[] []是错误的。

array2[0] = new int[3];

array2[1] = new int[6];   ...

2.二维数组的长度

int [][] x =new int [3][4];

x.length = 3 ;

x[0].length = x[1].length = x[2].length =4;

例子：选择题测验得分。用随机函数生成N个同学的选择题答案，保存在二维数组里。再随机生成一个正确答案，计算每位同学的正确率。

package basic_practice_003;

public class N_array { //多选题测验评分例子

final static int countIssue = 9;

final static int countStudent = 6;

public static void main(String[] args) {

// TODO Auto-generated method stub

System.out.println(" 题目 ：1 2 3 4 5 6 7 8 9");

char [][]student = new char[countStudent][countIssue];

char []rightAnswer = new char[countIssue];

getAnswer(rightAnswer);

getAnswer(student,rightAnswer);

}

public static void getAnswer(char [][]m,char []rightAnswer){

for(int j=0;j

System.out.print("student " + j + ":");

for(int i=0;i

m[j][i]=getRandomAnswer();

System.out.print(m[j][i] + " ");

}

int right =0;

for(int i=0;i

if(m[j][i]==rightAnswer[i]) right++;

}

System.out.printf(" right rate = %.3f",right*1.0/countIssue);

System.out.println();

}

}

public static void getAnswer(char []m){

System.out.print("rightAns :");

for(int i=0;i

m[i]=getRandomAnswer();

System.out.print(m[i] + " ");}

System.out.println();

}

public static char getRandomAnswer(){

return(char)('A' + Math.random()*('D' - 'A' + 1));}

}

结果：

输入N点坐标点，找出距离最小的两点。

public class FindNearestPoints {

public static void main(String[] args) {

// TODO Auto-generated method stub

System.out.println("1.enter the number of point:");

Scanner input = new Scanner(System.in);

int number_of_point = input.nextInt();

System.out.println("2.enter " +2*number_of_point +" point:");

double [][] point = new double[number_of_point][2];

System.out.println("enter "+ number_of_point*2+" points location:");

for(int i=0;i

point[i][0] = input.nextDouble();

point[i][1] = input.nextDouble();

}

double nearestD = (point[0][0]-point[1][0])*(point[0][0]-point[1][0])+(point[0][1]-point[1][1])*(point[0][1]-point[1][1]);

int index1=0,index2=0;

for(int i=0;i

for(int j=i+1;j

double Distance = (point[i][0]-point[j][0])*(point[i][0]-point[j][0])+(point[i][1]-point[j][1])*(point[i][1]-point[j][1]);

if(Distance < nearestD) {

nearestD=Distance;

index1=i;

index2=j;

}

}

}

System.out.printf("the NearestPoints is (%.2f,%.2f),(%.2f,%.2f)",point[index1][0],point[index1][1],point[index2][0],point[index2][1] );

System.out.println();

System.out.println("the NearestD = " + Math.sqrt(nearestD));

}

}