java新手筆記4

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1.數組

import java.util.Random;public class ArrayDemo1 {public static void main(String[] args) {int a = 10;int b = 20;////數組對象  建立10個變數  arr[0]、arr[1]、arr[2]、arr[3]...、arr[9]int[] arr = new int[10];//預設0arr[0] = 35;arr[1] = 29;System.out.println("arr[0] = " + arr[0]);System.out.println("arr[1] = " + arr[1]);//利用for逐一查看數組for(int i = 0; i < 10; i++ ) {System.out.print("arr[1] = " + arr[i] + "\t");}System.out.println("===================");Random ran = new Random();for(int i = 0; i < 10; i++ ){            arr[i] = ran.nextInt(101);System.out.println("arr["+i+"] = " + arr[i]);}//arr[10] = 100;//ArrayIndexOutOfBoundsException: 10//arr[9] = 3.14;類型匹配Random[] r = new Random[3];r[1] = ran;}}

 2.改變長度

import java.util.Random;public class ArrayDemo2 {public static void main(String[] args) {Random ran = new Random();int[] a = new int[8];for(int i = 0; i < a.length; i++ ) {a[i] = ran.nextInt(41) + 60;}for(int i = 0; i < a.length; i++ ){            System.out.println("a["+i+"] = " + a[i]);}System.out.println("--------------------");a = new int[5];//改變長度 length屬性for(int i = 0; i < a.length; i++ ){            System.out.println("a["+i+"] = " + a[i]);}}}

 3.初始化

import java.util.Random;public class ArrayDemo3 {public static void main(String[] args) {Random ran = new Random();//double[] a = new double[]{3.14, 98, 5.23, 6.14, 100};//數組初始化//char[] a = {‘中‘,‘國‘,‘影‘,‘分‘,‘身‘,‘B‘,‘w‘};//建立對象/*String s = new String("yema");String[] a = null;//對象可以null//int b = null;a = new String[8];a[3] = s;*/String[] a = {"javase","oracle","java web"};for(int i = 0; i < a.length; i++ ){            System.out.println("a["+i+"] = " + a[i]);}}}

 4.數組遍曆

import java.util.Random;public class ArrayDemo4 {public static void main(String[] args) {Random ran = new Random();int[][] a = new int[3][4];//3行 4列        //System.out.println("a.length = " + a.length);//System.out.println("a[1].length = " + a[1].length);//賦值for(int i = 0; i < a.length; i++ ){            for(int j = 0; j < a[i].length; j++) {               a[i][j] = ran.nextInt(101);}}//輸出for(int i = 0; i < a.length; i++ ){ for(int j = 0; j < a[i].length; j++) {//System.out.print("a["+i+"]["+j+"] = " + a[i][j] + "  ");System.out.print( a[i][j] + "  ");}System.out.println();}}}

 5.二維數組

import java.util.Random;public class ArrayDemo5 {public static void main(String[] args) {Random ran = new Random();int[][] a = new int[3][];//3行 a[0] = new int[]{18};int[] k = {20,50,90};a[1] = k;a[2] = new int[]{100,300};        //輸出for(int i = 0; i < a.length; i++ ){ for(int j = 0; j < a[i].length; j++) {System.out.print( a[i][j] + "  ");}System.out.println();}String[][] s = { //賦初值              {"javaEE","hibernate","spring"},              {"struts","jquery"}};        s[1][1] = "yema";        //輸出for(int i = 0; i < s.length; i++ ){ for(int j = 0; j < s[i].length; j++) {System.out.print( s[i][j] + "  ");}System.out.println();}}}

 

java新手筆記4