java基础：3.2 多维数组

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<countStudent;j++) {
			System.out.print("student " + j + ":");
			for(int i=0;i<countIssue;i++) {
				m[j][i]=getRandomAnswer();
				System.out.print(m[j][i] + " ");
				}
			int right =0;
			for(int i=0;i<countIssue;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<countIssue;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<number_of_point;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<number_of_point;i++) {
			for(int j=i+1;j<number_of_point;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));		
	}
}