Learning javase Arrays

Source: Internet
Author: User
Tags array length

Basic concepts of one-dimensional arrays

1. Only one type is allowed in the array (can be a parent-child relationship).

2, the array is the object.
Cases:

    int[ ] arrs={0,1,2};//arrs即一个对象。

3, the array is fixed-length, can not be increased or decreased.

4, declaration array: int[] arrs; The format is: array element type [] array name;
Creating a one-dimensional array must declare the array length: int[] Arrs = new Int[3];

5, initialize the array, if the value is not initialized, the system defaults to 0.
Example of initialization:

    int arr1 = {1,2,3,5,25};(推荐)    int arr2 = new int[] {1,2,3,5,25};

6, the array element Subscript (index) is calculated starting from 0.

Basic Method Array Traversal:
public class Test {    public static void main(String[] args) {        int[] arrs4 = {1,2,3,4,5,6,7,8};        System.out.println("倒序遍历:");        for(int i = arrs4.length-1;i>=0;i--) {            System.out.println(arrs4[i]);        }        System.out.println("foreach遍历:");        for (int arr:arrs4             ) {            System.out.println(arr);//快捷键:sout        }        System.out.println("for遍历:");        for(int i =0;i<arrs4.length;i++) {            System.out.println(arrs4[i]);        }        System.out.println("while遍历");        int k =0;        while(k<arrs4.length) {            System.out.println(arrs4[k]);            k++;        }        System.out.println("do while遍历");        int u =0;        do {            System.out.println(arrs4[u]);            u++;        }while (u<arrs4.length                );          }}
Arrays class

Arrays class: Tool class, Operation array used.
Arrays.fill: array element substitution.
Arrays.copyof: array element copy.
Arrays.binarysearch: array element index.

public class test3 {    public static void main(String[] args) {        int[] arrs = {1,2,3,4};        System.out.println("替换前:"+Arrays.toString(arrs));        Arrays.fill(arrs,2,3,2);        System.out.println("替换后:"+Arrays.toString(arrs));        int[] arrs1 = {1,2,3,4,0,5,4,1,2};        System.out.println("排序前:"+Arrays.toString(arrs1));        Arrays.sort(arrs1);        System.out.println("排序后:"+Arrays.toString(arrs1));        int[] arrs2 = {1,2,3};        int[] arrs21 = new int [4];        System.out.println("复制前"+Arrays.toString(arrs2));        arrs21 = Arrays.copyOf(arrs2,4);        System.out.println("复制后"+Arrays.toString(arrs21));        int[] arrs3 = {1,2,3};        System.out.println(Arrays.binarySearch(arrs3,3));//返回值是元素索引    }}
Basic concepts of two-dimensional arrays

Define a two-dimensional array, at least specify rows, and you can specify no columns.

int[][] arrays = new int[3][];
Basic Method Array Traversal:
public class test2 {    public static void main(String[] args) {        //定义一个数组:        int [][] arrs1= new int[3][];        int[][]arrs2 = {{1,2,3},{2,4},{3,5}};        System.out.println("foreach遍历:");        for (int[] arrs3:arrs2             ) {            for (int arrs4:arrs3                 ) {                System.out.print(arrs4+"\t");            }            System.out.println();        }        System.out.println("for遍历");        for(int i=0;i<arrs2.length;i++) {            for(int j=0;j<arrs2[i].length;j++) {                System.out.print(arrs2[i][j]+"\t");            }            System.out.println();        }        System.out.println("while遍历");        int k = 0;        while(k<arrs2.length) {            int u =0;            while (u<arrs2[k].length) {                System.out.print(arrs2[k][u]+"\t");                u++;            }            System.out.println();            k++;        }    }}

Learning javase Arrays

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