Core Java (五) Java数组
数组的初始化和拷贝
package com.xujin;
import java.util.Arrays;
public class Test {
public static void main(String[] args){
int[] a = {2, 3, 5, 7};
int[] b = a;//此时a与b引用同一个数组
System.out.println(Arrays.toString(a));//[2, 3, 0, 7]
System.out.println(Arrays.toString(b));//[2, 3, 0, 7]
b = new int[]{12, 13, 14};//用一个匿名数组初始化b
System.out.println(Arrays.toString(a));//[2, 3, 0, 7]
System.out.println(Arrays.toString(b));//[12, 13, 14]
//public static int[] copyOf(int[] original, int newLength)
int[] c = Arrays.copyOf(a, a.length);
c[2] = 100;
System.out.println(Arrays.toString(a));//[2, 3, 0, 7]
System.out.println(Arrays.toString(c));//[2, 3, 100, 7]
//public static void arraycopy(Object src, int srcPos, Object dest, int destPos, int length)
int[] d = {33, 44, 55, 66, 77, 88, 99};
System.arraycopy(d, 0, a, 1, 3);
System.out.println(Arrays.toString(a));//[2, 33, 44, 55]
System.out.println(Arrays.toString(d));//[33, 44, 55, 66, 77, 88, 99]
//public static int[] copyOfRange(int[] original, int from, int to)
int[] e = Arrays.copyOfRange(a, 1, 3);
System.out.println(Arrays.toString(e));//[33, 44]
}
}
数组的排序
本测试在0~49共50个数里面任取6个数，按大小排序好了输出
package com.xujin;
import java.util.Arrays;
public class Test {
static final int MAX = 50;
static final int FIT = 6;
public static void main(String[] args){
int[] total = new int[MAX];
int[] result = new int[FIT];
for(int i = 0; i < MAX; i++)
total[i] = i;
for(int i = 0; i < FIT; i++){
result[i] = (int) (Math.random() * MAX);
}
Arrays.sort(result);
System.out.println(Arrays.toString(result));
}
}
数组的二分搜索，填充，以及判数组是否相同的测试
package com.xujin;
import java.util.Arrays;
public class Test {
public static void main(String[] args){
int[] a = new int[100];
for(int i = 0; i < a.length; i++)
a[i] = i;
int[] b = Arrays.copyOfRange(a, 0, 10);
System.out.println(Arrays.toString(b));//[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
//public static int binarySearch(int[] a, int key)
int r = Arrays.binarySearch(a, 23);
System.out.println(r);//23
//public static void fill(int[] a, int val)
Arrays.fill(b, 8);
System.out.println(Arrays.toString(b));//[8, 8, 8, 8, 8, 8, 8, 8, 8, 8]
//public static boolean equals(int[] a, int[] a2)
int[] c = new int[]{8, 8, 8, 8, 8, 8, 8, 8, 8, 8};
if(Arrays.equals(b, c))//此时相等，返回一个true
System.out.println("两个数组大小相等，并且下表相同的元素都对应相等");
}
}
二维数组初探
package com.xujin;
import java.util.Arrays;
public class Test {
public static void main(String[] args){
int[][] matrix = {
{1,2,3},
{3,2,1},
{4,5,6},
};
System.out.println(matrix[0][2]); //3
for(int i = 0; i < matrix.length; i++)
System.out.println(Arrays.toString(matrix[i]));//[1, 2, 3]
//[3, 2, 1]
//[4, 5, 6]
//快速打印一个二维数组的数据元素列表
System.out.println(Arrays.deepToString(matrix));//[[1, 2, 3], [3, 2, 1], [4, 5, 6]]
//for each循环语句不能自动处理二维数组的每一个元素，他是按照一维数组处理的
for(int[] row : matrix)
for(int value : row){
System.out.println(value * 10);
}
/* 10
20
30
30
20
10
40
50
60
*/
}
}
不规则数组
打印出如下数列：
1
1 2
1 2 3
1 2 3 4
1 2 3 4 5
1 2 3 4 5 6
1 2 3 4 5 6 7
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9 10
package com.xujin;
public class Test {
public static void main(String[] args){
int[][] test = new int[10][];
for(int n = 0; n < 10; n++){
test[n] = new int[n + 1];
}
for(int i = 0; i < 10; i++)
for(int j = 0; j < test[i].length; j++){
test[i][j] = j + 1;
}
for(int[] row : test){
for(int value : row)
System.out.print(value + " ");
System.out.println();
}
}
}
上面的程序创建了一个不规则数组，该数组有10个元素，分别是test[0]~test[9]，每个元素所包含的int型数不同，test[0]包含1个，test[1]包含2个....test[9]包含10个