内存分析
见图:
数组三种初始化
静态初始化
int[] a = {
1,2,3};
Man[] mans = {
new Man(1,1),new Man(2,2)};
动态初始化
int[] a = new int[2];
a[0]=1;
a[1]=2;
数组的默认初始化
- 数组是引用类型,它的元素相当于类的实例变量,因此数组一经分配空间,其中的每个元素也被按照实例变量同样的方式被隐式初始化。
public class A0122Array {
public static void main(String[] args) {
//静态初始化,创建+赋值
int nums[] = {
1,2,3,4,5};
System.out.println(nums[2]);
//动态初始化,包含默认初始值
//int[] nums1;
//nums1 =new int[5];
int[] nums1 = new int[5];
nums1[0]=2;
nums1[1]=4;
nums1[2]=6;
nums1[3]=8;
System.out.println(nums1[3]);
System.out.println(nums1[4]);//有默认初始值 int的初始值为0
}
}
run:
3
8
0
数组的四个基本特点:
数组的边界
public class A0122ArrayBounds {
public static void main(String[] args) {
int[] a=new int[5];
System.out.println(a[5]);
}
}
run:
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 5
at com.lingxiang.data.January.A0122ArrayBounds.main(A0122ArrayBounds.java:6)
Process finished with exit code 1
数组使用
For循环
public class A0122ArrayDemo1 {
public static void main(String[] args) {
//打印所有元素
int[] a = new int[5];
a[0]=1;
a[1]=2;
a[2]=3;
a[3]=4;
a[4]=5;
for (int i = 0; i <a.length; i++) {
System.out.println(a[i]);
}
System.out.println("=================");
//计算所有元素的总和
int sum =0;
for (int i = 0; i < a.length; i++) {
sum += a[i]; // sum=sum+a[i]; 和 sum += [i];是一样的意思
}
System.out.println(sum);
System.out.println("=================");
//查找最大的数
int max =a[0];
for (int i=1;i<a.length;i++){
if (a[i]>max){
max=a[i];}
}
System.out.println(max);
}
}
run:
1
2
3
4
5
=================
15
=================
5
For-Each 循环
public class A0122ArrayDemo2 {
public static void main(String[] args) {
int[] a = {
1,2,3,4,5};
//JDK1.5之后开始 没有下标
for (int i : a) {
System.out.println(i);
}
}
}
数组作方法入参
数组作返回值
public class A0122ArrayDemo2 {
public static void main(String[] args) {
int[] a = {
1, 2, 3, 4, 5};
//JDK1.5之后开始 没有下标
for (int i : a) {
System.out.println(i);
}
System.out.println("==============");
int[] b = {
2, 4, 6, 8};
printarray(b);
System.out.println("==============");
int[] reverseb = reverse(b);
printarray(reverseb);
System.out.println("==============");
int[] reverse1b = reverse1(b);
printarray(reverse1b);
}
//打印数组元素的方法
public static void printarray(int[] b) {
for (int i = 0; i < b.length; i++) {
System.out.print(b[i] + "\t");
}
System.out.println();
}
//反转数组 写法一
public static int[] reverse(int[] b) {
int[] c = new int[b.length];
for (int i = 0; i < b.length; i++) {
c[b.length - i - 1] = b[i];
}
return c;
}
//反转数组 写法二
public static int[] reverse1(int[] b) {
int[] c = new int[b.length];
for (int i = 0,j=c.length-1; i < b.length; i++,j--) {
c[j]=b[i];
}
return c;
}
}
run:
1
2
3
4
5
==============
2 4 6 8
==============
8 6 4 2
==============
8 6 4 2