Java数组算法（实用）

图片.png

数组知识导图

---

数组拷贝：
public class ShuZuTest {

//这样拷贝数组间没有隔离性
public static void test1(){
    String[] ss1 = {"1","2","3"};
    //把ss1对数组的引用传递给变量ss2，两个便令指向的是同一个数组
    String[] ss2 =ss1;
    ss2[0] = "张三";
    System.out.println(ss1[0]);//张三
}

//推荐
public static void test2(){
    String[] ss1 = {"1","2","3"};
    //通过new关键字在内存中开辟一块空间，ss2指向的是行的数组对象
    String[] ss2 = new String[ss1.length];
    for(int i = 0;i<ss2.length;i++){
        ss2[0] = "张三";
        System.out.println(ss1[0]);//1
    }
    
}
public static void test4(){
    String[] ss1 = {"1","2","3"};
    String[] ss2 =Arrays.copyOf(ss1, ss1.length);
    System.out.println(Arrays.toString(ss2));//[1,2,3]
}

//=========================================================
//数组扩容：
public static void test5(){
    String[] array1 = {"1","2","3"};
    array1 = Arrays.copyOf(array1, array1.length+2);
    System.out.println(Arrays.toString(array1));//[1,2,3,null,null]
}
//例子：统计字符的位置
public static void test6(){
    String str = "统计一个字符串的位置而已";
    int[] ary = countAll(str, '符');//
    System.out.println(Arrays.toString(ary));
}
public static int[] countAll(String str,char ch){
    int[] array = {};//创建一个空数组
    for(int i=0;i<str.length();i++){
        if(ch == str.charAt(i)){
            array = Arrays.copyOf(array, array.length+1);
            array[array.length-1] = i;
        }
    }
    return array;
}

}