C,C++的数组都可以分配在栈上,
但是java的数组属于引用类型.
一位数组的声明方式:
type var[]; 或者type[] var;
例如:
int a[]; int[] a2;
Person[] p1; String s1[];
java语言声明数组的时候, 不能指定其长度,例如 int a[5]; //错误的
java的数组是new出来的.
int[] s=new int[5]; //其中s放在栈里, 5个0放在堆里.
for(int i=0;i<5;i++){
s[i]=i;
}
数组的动态初始化:
public class Test
{
public static void main(String[] args)
{
int a[];
a=new int[3];
a[0] = 3; a[1] = 9; a[2] = 8;
Date days[];
days=new Date[3];
days[0] = new Date(1,4,2004);
days[1] = new Date(2,4,2004);
days[2] = new Date(3,4,2004);
}
}
class Date{
int year, month, day;
Date(int y, m, d){
year = y;
month = m;
day = d;
}
}
数组的静态初始化:
public class Test
{
public static void main(String[] args)
{
int a[] = {3, 9, 8};
Date days[] = {
new Date(1,4,2004),
new Date(2,4,2004),
new Date(3,4,2004)
};
}
class Date{
int year, month, day;
Date(int y, m, d){
year = y;
month = m;
day = d;
}
}
数组元素的默认初始化: 对象是null, int 是 0.
数组元素的访问: a[3], c[6*i].
数组的下标范围:0~n-1.
数组的长度: a.length, 注意是属性, 不是方法. 而String的length()是方法.
public class TestArray {
public static void main(String[] args){
int a[]={2,4,5,8};
for(int i=0;i<a.length;i++)
System.out.println(a[i]+" ");
}
}
args的详细用法:
public class TestArgs {
public static void main(String[] args) {
/*
for(int i=0; i<args.length; i++) {
System.out.println(args[i]);
}
System.out.println(
"Usage: java Test "n1" "op" "n2"");
*/
if(args.length<3){
System.out.println(
"Usage: java Test "n1" "op" "n2"");
System.exit(-1);
}
double d1 = Double.parseDouble(args[0]);
double d2 = Double.parseDouble(args[2]);
double d = 0;
if(args[1].equals("+")) d = d1+d2;
else if(args[1].equals("-")) d = d1-d2;
else if(args[1].equals("x")) d = d1*d2;
else if(args[1].equals("/")) d = d1/d2;
else{
System.out.println("Error operator!");
System.exit(-1);
}
System.out.println(d);
}
}
基础类型都分配在栈上, 如果想让它存放在堆里, 要把他包装成一个类:
Double.ParseDouble();
选择排序数组的例子:
public class NumSort {
public static void main(String[] args) {
int[] a = new int[args.length];
for (int i=0; i<args.length; i++) {
a[i] = Integer.parseInt(args[i]);
}
print(a);
selectionSort(a);
print(a);
}
private static void selectionSort(int[] a) {
int k, temp;
for(int i=0; i<a.length; i++) {
k = i;
for(int j=k+1; j<a.length; j++) {
if(a[j] < a[k]) {
k = j;
}
}
if(k != i) {
temp = a[i];
a[i] = a[k];
a[k] = temp;
}
}
}
private static void print(int[] a) {
for(int i=0; i<a.length; i++) {
System.out.print(a[i] + " ");
}
System.out.println();
}
}
冒泡排序Date的算法:
public class TestDateSort {
public static void main(String[] args) {
Date[] days = new Date[5];
days[0] = new Date(2006, 5, 4);
days[1] = new Date(2006, 7, 4);
days[2] = new Date(2008, 5, 4);
days[3] = new Date(2004, 5, 9);
days[4] = new Date(2004, 5, 4);
Date d = new Date(2006, 7, 4);
String str = String.valueOf(d);
//str = d.toString();
bubbleSort(days);
for(int i=0; i<days.length; i++) {
System.out.println(days[i]);
}
System.out.println(binarySearch(days, d));
}
public static Date[] bubbleSort(Date[] a){
int len = a.length;
for(int i = len-1;i>=1;i--){
for(int j = 0;j<=i-1;j++){
if(a[j].compare(a[j+1]) > 0){
Date temp = a[j];
a[j]=a[j+1];
a[j+1]=temp;
}
}
}
return a;
}
public static int binarySearch(Date[] days, Date d) {
if (days.length==0) return -1;
int startPos = 0;
int endPos = days.length-1;
int m = (startPos + endPos) / 2;
while(startPos <= endPos){
if(d.compare(days[m]) == 0) return m;
if(d.compare(days[m]) > 0) {
startPos = m + 1;
}
if(d.compare(days[m]) < 0) {
endPos = m -1;
}
m = (startPos + endPos) / 2;
}
return -1;
}
}
class Date {
int year, month, day;
Date(int y, int m, int d) {
year = y; month = m; day = d;
}
public int compare(Date date) {
return year > date.year ? 1
: year < date.year ? -1
: month > date.month ? 1
: month < date.month ? -1
: day > date.day ? 1
: day < date.day ? -1 : 0;
}
public String toString() {
return "Year:Month:Day -- " + year + "-" + month + "-" + day;
}
}
500个人一圈, 数到3退出, 最后剩几号:
public class Count3Quit {
public static void main(String[] args) {
boolean[] arr = new boolean[500];
for(int i=0; i<arr.length; i++) {
arr[i] = true;
}
int leftCount = arr.length;
int countNum = 0;
int index = 0;
while(leftCount > 1) {
if(arr[index] == true) {
countNum ++;
if(countNum == 3) {
countNum = 0;
arr[index] = false;
leftCount --;
}
}
index ++;
if(index == arr.length) {
index = 0;
}
}
for(int i=0; i<arr.length; i++) {
if(arr[i] == true) {
System.out.println(i);
}
}
}
}