07-13_01数组

数组

数组声明创建

public static void main(String[] args) {
        //变量的类型    变量的名字  =   变量的值
        //数组类型
        int[] nums;//声明一个数组
        nums = new int[10];//创建一个数组
        //int [] nums = new int[10];
        nums[0]=1;
        nums[1]=2;
        nums[2]=3;
        nums[3]=4;
        nums[4]=5;
    	//计算所有变量的和
        int sum = 0 ;
    	//获取数组的长度，arrays.length
        for (int i = 0; i < nums.length;i++){
            sum+=nums[i];
        }
        System.out.println(sum);
    }

---

数组的使用

public static void main(String[] args) {
    int[] arrays = {1,2,3,4,5};

    //打印全部的数组元素
    for (int i = 0; i < arrays.length; i++) {
        System.out.println(arrays[i]);
    }
    System.out.println("====================");
    //计算所有元素的和；
    int sum = 0;
    for (int i = 0; i < arrays.length; i++) {
        sum += arrays[i];
    }
    System.out.println("sum="+sum);
    System.out.println("====================");

    //查找最大元素
    int max = arrays[0];

    for (int i = 1; i < arrays.length; i++) {
        if(arrays[i]>max){
            max = arrays[i];
        }
    }
    System.out.println("max="+max);
}

数组反转实例：

public static void main(String[] args) {
        int [] arrays = {1,2,3,4,5};

//        //没有下标
//        for (int array : arrays) {
//            System.out.println(array);
//        }

       // printArray(arrays);
        int[] reverse = reverse(arrays);
        printArray(reverse);
    }
    //反转数组
    public static int[] reverse(int[] arrays){
        int[] result = new int[arrays.length];
        //反转的操作
        for (int i = 0,j=result.length-1; i < arrays.length; i++,j--) {
            result[j] = arrays[i];
        }
        return result;
    }
    //打印数组元素
    public static void printArray(int[] arrays){
        for (int i = 0; i < arrays.length; i++) {
            System.out.print(arrays[i]+" ");
        }
    }

---

多维数组

public static void main(String[] args) {
    int [][] array ={{1,2},{2,3},{3,4},{4,5}};

    for (int i = 0; i < array.length; i++) {
        for (int j = 0; j < array[i].length; j++) {
            System.out.println("下标为"+i+"的数组的下标为"+j+"的元素为"+array[i][j]);
        }
    }
}
//打印数组元素
public static void printArray(int[] arrays){
    for (int i = 0; i < arrays.length; i++) {
        System.out.print(arrays[i]+" ");
    }
}

---

Array类

public static void main(String[] args) {
    int[] a = {1,2,3,4,9090,31231,543,21,3,23};
    System.out.println(a); // [I@4554617c
    //打印数组元素Arrays.toString
    System.out. println(Arrays.toString(a));
    printArray(a);
}
private static void printArray(int[] a) {
    for (int i = 0; i < a.length; i++) {
        if(i==0){
            System.out.print("[");
        }
        if(i==a.length-1){
            System.out.print(a[i]+"]");
        }else {
            System.out.print(a[i]+" ,");
        }
    }
}

冒泡数组

public static void main(String[] args) {
    int [] a = {1,4,5,2,5,5,5,1,1,5};
    int [] sort = sort(a);
    System.out.println(Arrays.toString(sort));
}
public static int[] sort(int[] array){
    int temp = 0;
    for (int i = 0; i < array.length-1; i++) {

        for (int j = 0; j < array.length - 1 - j; j++) {
            if(array[j+1]<array[j]){
                temp = array[j];
                array[j] = array[j+1];
                array[j+1] = temp;
            }
        }
    }
    return array;
}

---

稀疏数组

public static void main(String[] args) {
    int [][] array1 = new int[11][11];
    array1[1][2]=1;
    array1[2][3]=2;
    System.out.println("输出原始的数组");
    for (int[] ints : array1) {
        for (int anInt : ints) {
            System.out.print(anInt+"\t");
        }
        System.out.println();
    }
    System.out.println("===============");
    int sum = 0;
    for (int i = 0; i < 11; i++) {
        for (int j = 0; j < 11; j++) {
            if(array1[i][j]!=0){
                sum++;
            }
        }
    }
    System.out.println("有效值的个数："+sum);
    //2.创建一个稀疏数组
    int [][] array2 = new int[sum+1][3];
    array2[0][0] = 11;
    array2[0][1] = 11;
    array2[0][2] = sum;
    //遍历二维数组，将非零的值，存放稀疏数组中
    int count=0;
    for (int i = 0; i < array1.length; i++) {
        for (int j = 0; j < array1[i].length; j++) {
            if(array1[i][j]!=0){
                count++;
                array2[count][0] = i;
                array2[count][1] = j;
                array2[count][2] = array1[i][j];
            }
        }
    }
    //输出稀疏数组
    System.out.println("稀疏数组");
    for (int i = 0; i < array2.length; i++) {
        System.out.println(array2[i][0]+"\t"
                +array2[i][1]+"\t"
                +array2[i][2]+"\t");
    }
    System.out.println("=============");
    System.out.println("还原");
    //1.读取稀疏数组
    int[][]  array3 = new int[array2[0][0]][array2[0][1]];
    //2.给其中的元素还原它的值
    for (int i = 1; i < array2.length; i++) {
        array3[array2[i][0]][array2[i][1]] = array2[i][2];
    }
    //打印
    System.out.println("输出还原的数组");
    for (int[] ints : array3) {
        for (int anInt : ints) {
            System.out.print(anInt+"\t");
        }
        System.out.println();
    }
}