老
老戴
V1
2023/02/15阅读:13主题:默认主题
给list加一个对象放第一位如何操作?
给list加一个对象放第一位如何操作?
结论:使用List接口的void add(int index, E element) 方法,list.add(0, obj) ;
代码:
@Test
public void addTest(){
List<Obj> list = new ArrayList<>();//或LinkedList
list.add(new Obj("a"));
list.add(new Obj("b"));
System.out.println("before list = " + list);
list.add(0, new Obj("c"));
System.out.println("after list = " + list);
}
class Obj {
private String name;
public Obj(String name) {
this.name = name;
}
@Override
public String toString() {
return "Obj{" +
"name='" + name + ''' +
'}';
}
}
/*
结果:
before list = [Obj{name='a'}, Obj{name='b'}]
after list = [Obj{name='c'}, Obj{name='a'}, Obj{name='b'}]
Obj不重写toString
before list = [wcd.day1210.Test1$Obj@482cd91f,wcd.day1210.Test1$Obj@123f1134]
after list = [wcd.day1210.Test1$Obj@7d68ef40, wcd.day1210.Test1$Obj@482cd91f, wcd.day1210.Test1$Obj@123f1134]
*/
-
对象地址未变,使用的是浅拷贝
作者介绍
老
老戴
V1