Java学习笔记--Arrays类
转载：http://plseye.iteye.com/blog/255698
int[] s1={1,2,3,4,5,6};
System.out.printf("操作前 (原件)\t%s%n", Arrays.toString(s1));
int s2[] = Arrays.copyOf(s1, 4);//只复制前4个数据
System.out.printf("操作前 (副本)\t%s%n", Arrays.toString(s2));
s2[0] = 10;
s2[1] = 20;
s2[2] = 30;
s2[3] = 40;
System.out.printf("操作后 (原件)\t%s%n", Arrays.toString(s1));//对复制后的数组的操作不影响源数组
System.out.printf("操作后 (副本)\t%s%n", Arrays.toString(s2));
int s3[] = Arrays.copyOf(s1, 7);////复制s1全部数据，并增加容量
s3[6]=7;
System.out.printf("操作后 (副本)\t%s%n", Arrays.toString(s3));
int s4[] = Arrays.copyOfRange(s1, 2,10);//根据范围复制s1数据
System.out.printf("操作后 (副本)\t%s%n", Arrays.toString(s4));
结果：
操作前 (原件) [1, 2, 3, 4, 5, 6]
操作前 (副本) [1, 2, 3, 4]
操作后 (原件) [1, 2, 3, 4, 5, 6]
操作后 (副本) [10, 20, 30, 40]
操作后 (副本) [1, 2, 3, 4, 5, 6, 7]
操作后 (副本) [3, 4, 5, 6, 0, 0, 0, 0]
转载：http://www.blogjava.net/gdws/articles/321391.html
有的时候需要对数组里的element进行排序。当然可以自己编写合适的排序方法，但既然java包里有自带的Arrays.sort排序方法，在数组元素比较少的时候为何不用？
Sorting an Array 1. 数字排序 int[] intArray = new int[] { 4, 1, 3, -23 };
Arrays.sort(intArray);
输出： [-23, 1, 3, 4]
2. 字符串排序，先大写后小写 String[] strArray = new String[] { "z", "a", "C" };
Arrays.sort(strArray);
输出： [C, a, z]
3. 严格按字母表顺序排序，也就是忽略大小写排序 Case-insensitive sort
Arrays.sort(strArray, String.CASE_INSENSITIVE_ORDER);
输出： [a, C, z]
4. 反向排序， Reverse-order sort
Arrays.sort(strArray, Collections.reverseOrder());
输出：[z, a, C]
5. 忽略大小写反向排序 Case-insensitive reverse-order sort
Arrays.sort(strArray, String.CASE_INSENSITIVE_ORDER);
Collections.reverse(Arrays.asList(strArray));
输出： [z, C, a]
java初学者最常见的错误思想，就是试图去写一些方法来完成数组的排序功能，其实，数组排序功能，在java的api里面早已实现，我们没有必要去重复制造轮子。
Arrays类有一个静态方法sort,利用这个方法我们可以传入我们要排序的数组进去排序，因为我们传入的是一个数组的引用，所以排序完成的结果也通过这个引用的来更改数组.对于整数、字符串排序，jdk提供了默认的实现，如果要对一个对象数组排序，则要自己实现java.util.Comparator接口。
package demo1.client;
import java.util.Arrays;
import java.util.Comparator;
public class ArraySortDemo {
public void sortIntArray() {
int[] arrayToSort = new int[] { 48, 5, 89, 80, 81, 23, 45, 16, 2 };
System.out.println("排序前");
for (int i = 0; i < arrayToSort.length; i++)
System.out.println(arrayToSort[i]);
// 调用数组的静态排序方法sort
Arrays.sort(arrayToSort);
System.out.println("排序后");
for (int i = 0; i < arrayToSort.length; i++)
System.out.println(arrayToSort[i]);
}
public void sortStringArray() {
String[] arrayToSort = new String[] { "Oscar", "Charlie", "Ryan",
"Adam", "David" };
System.out.println("排序前");
for (int i = 0; i < arrayToSort.length; i++)
System.out.println(arrayToSort[i]);
System.out.println("排序后");
//调用数组的静态排序方法sort
Arrays.sort(arrayToSort);
for (int i = 0; i < arrayToSort.length; i++)
System.out.println(arrayToSort[i]);
}
public void sortObjectArray() {
Dog o1 = new Dog("dog1", 1);
Dog o2 = new Dog("dog2", 4);
Dog o3 = new Dog("dog3", 5);
Dog o4 = new Dog("dog4", 2);
Dog o5 = new Dog("dog5", 3);
Dog[] dogs = new Dog[] { o1, o2, o3, o4, o5 };
System.out.println("排序前");
for (int i = 0; i < dogs.length; i++) {
Dog dog = dogs[i];
System.out.println(dog.getName());
}
Arrays.sort(dogs, new ByWeightComparator());
System.out.println("排序后：");
for (int i = 0; i < dogs.length; i++) {
Dog dog = dogs[i];
System.out.println(dog.getName());
}
}
public static void main(String[] args) {
ArraySortDemo t = new ArraySortDemo();
t.sortIntArray();
t.sortStringArray();
t.sortObjectArray();
}
}
class Dog {
private String name;
private int weight;
public Dog(String name, int weight) {
this.setName(name);
this.weight = weight;
}
public int getWeight() {
return weight;
}
public void setWeight(int weight) {
this.weight = weight;
}
public void setName(String name) {
this.name = name;
}
public String getName() {
return name;
}
}
class ByWeightComparator implements Comparator {
public final int compare(Object pFirst, Object pSecond) {
int aFirstWeight = ((Dog) pFirst).getWeight();
int aSecondWeight = ((Dog) pSecond).getWeight();
int diff = aFirstWeight - aSecondWeight;
if (diff > 0)
return 1;
if (diff < 0)
return -1;
else
return 0;
}
}
更多：http://docs.oracle.com/javase/6/docs/api/
