List Slice in Python(Compared with Java)

Python:　　

　　在Python中, 对于list, 切片会返回一个新的list, 而不会改变原有的list. 注意这儿说的"不会改变原有的list"指的是下面的这种情况: 

a = [10, 20, 30]
b = a[1:3]
print('a is {0}'.format(a))
print('b is {0}'.format(b))

print('Change b---------------')
b[0] = 8
print('a is {0}'.format(a))
print('b is {0}'.format(b))

print('Change a---------------')
a[1] = 1024
print('a is {0}'.format(a))
print('b is {0}'.format(b))

　　Output:

a is [10, 20, 30]
b is [20, 30]
Change b---------------
a is [10, 20, 30]
b is [8, 30]
Change a---------------
a is [10, 1024, 30]
b is [8, 30]

　　从上面的代码以及输出结果中, 我们可以看出, 执行完"b = a[1:3]"后, 更改a或b中任何一个都不会对另外一个有影响.

　　请注意上面说的这种情况与下面这种情况的区别:

def change(x):
　　x[1:3] = ['a', 'b']

a = [10, 20, 30]
print('a is {0}'.format(a))
change(a)
print('a is {0}'.format(a))

　　Output:

a is [10, 20, 30]
a is [10, 'a', 'b']

 

Java:

　　现在让我们来看看Java中的'切片'操作(这里指的是List接口中的subList()方法)与Python中的切片操作的区别:  (此处把

Java的subList()搬出来, 仅仅是为了对比一下,让大家更好的理解Python中的list切片"不会改变原有的list"这句话)

public static void main(String[] args){
        List<Integer> alist = new ArrayList<Integer>();
        for (int i = 0; i < 10; ++i){
            alist.add(i);
        }
        List<Integer> blist = alist.subList(1, 5);
        System.out.println("alist:\n" + alist);
        System.out.println("blist:\n" + blist);
        System.out.println();

        System.out.println("change alist----------------");
        alist.set(1, 888);
        System.out.println("alist:\n" + alist);
        System.out.println("blist:\n" + blist);
        System.out.println();

        System.out.println("change blist----------------");
        blist.set(1, 1024);
        System.out.println("alist:\n" + alist);
        System.out.println("blist:\n" + blist);
    }

　　Output:

alist:
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
blist:
[1, 2, 3, 4]

change alist----------------
alist:
[0, 888, 2, 3, 4, 5, 6, 7, 8, 9]
blist:
[888, 2, 3, 4]

change blist----------------
alist:
[0, 888, 1024, 3, 4, 5, 6, 7, 8, 9]
blist:
[888, 1024, 3, 4]

　　从上面的代码以及输出结果中, 我们可以看出, 执行完"List<Integer> blist = alist.subList(1, 5);"后, 更改alist或blist中任何一个,

都会对另外一个有影响.