<!doctype html>java对象集合学习记录
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:root { --accent-color: #aeb1b5; --dark-accent-color: #787a7c; --background-color: white; --border-color: #ddd; --code-bg-color: #f8f8f8; --font-color: #42464c; --header-color: #222324; --link-color: #2077b2; --control-text-color: #667176; --side-bar-bg-color: #fafafa; --body-font: "Iosevka", "Fira Mono", "Source Code Pro", Courier, monospace; --header-font: "Fira Sans", "Roboto", "Source Sans Pro", sans-serif; --border-radius: 2px; --document-horizontal-margin: 80px; --document-padding-x: 10ch; --font-size: 16px; --h1-fontsize: 2rem; --h2-fontsize: 1.375rem; --h3-fontsize: 1.25rem; --h4-fontsize: 1.125rem; --line-height: 1.4; --main-content-margin: 0 auto; --main-content-max-width: 100ch; --monospace-font-size: 15px; --monospace-font: "Iosevka", "Fira Mono", "Source Code Pro", Courier, monospace; --monospace-line-height: 1.4; --monospace: var(--monospace-font); --nav-width: 200px; --vertical-padding: 40px; }
@media (max-width: 640px) {
:root { --document-padding-x: 4ch; }
}
html { font-size: var(--font-size); background-color: var(--background-color); }
html, body { color: var(--font-color); font-family: var(--body-font); line-height: var(--line-height); }
#write { padding-left: var(--document-padding-x); padding-right: var(--document-padding-x); max-width: var(--main-content-max-width); box-sizing: border-box; }
pre.md-meta-block { background-color: var(--background-color); padding-bottom: 0.5rem; color: var(--accent-color); border-bottom: 2px solid var(--border-color); font-family: var(--monospace-font); }
h1, h2, h3, h4, h5, h6 { font-family: var(--header-font); font-weight: bold; color: var(--header-color); }
h1 { margin-top: 3rem; margin-bottom: 1.5rem; font-size: var(--h1-fontsize); }
h1:not(:first-child) { margin-top: 3rem; }
h2 { margin-top: 1.5rem; margin-bottom: 1.5rem; font-size: var(--h2-fontsize); }
h3 { margin-top: 1.5rem; margin-bottom: 1rem; font-size: var(--h3-fontsize); }
h4, h5, h6 { color: var(--header-color); margin-top: 1rem; margin-bottom: 0rem; font-size: 1rem; }
h4 { font-size: var(--h4-fontsize); }
h6 { color: var(--control-text-color); }
h1 tt, h1 code { font-size: inherit; }
h2 tt, h2 code { font-size: inherit; }
h3 tt, h3 code { font-size: inherit; }
h4 tt, h4 code { font-size: inherit; }
h5 tt, h5 code { font-size: inherit; }
h6 tt, h6 code { font-size: inherit; }
table { margin-top: 1rem; margin-bottom: 1rem; }
table tr:nth-child(2n), thead { background-color: var(--side-bar-bg-color); }
td, th { border-style: solid; border-color: var(--border-color); border-width: 1px; padding: 0.35rem 0.7rem; }
li p { margin: 0px; }
.task-list { padding-left: 0px; }
.task-list-item { padding-left: 1.5em; margin-bottom: 0rem; }
#write input[type="checkbox"] { margin-top: 5px; }
blockquote { margin: 1rem 0px 1rem 0.5ch; padding-left: 2ch; position: relative; overflow: hidden; border-left: 2px solid var(--border-color); color: var(--accent-color); }
hr { border-top: none; border-right: none; border-left: none; border-image: initial; border-bottom: 2px solid var(--border-color); margin-top: 1.4rem; margin-bottom: 1.4rem; }
p { margin: 1rem 0px; }
.cm-s-inner .CodeMirror-gutters { background: var(--code-bg-color); }
.code-tooltip { box-shadow: none; border-radius: var(--border-radius); background-color: var(--code-bg-color); border-color: var(--border-color); border-style: solid; border-width: 1px; }
.code-tooltip input { outline: none; width: 20ch; }
.md-fences .code-tooltip { bottom: -1.8rem; }
.md-fences.md-focus .cm-s-inner { border-bottom-right-radius: 0px; }
.autoComplt-hint { background-color: transparent !important; margin: 0px !important; padding: 0.125rem 0.375rem !important; color: var(--text-color) !important; line-height: var(--line-height) !important; height: 1.4rem !important; }
.autoComplt-hint-selected { background-color: var(--link-color) !important; color: var(--background-color) !important; }
.md-fences, code, tt { border: 1px solid var(--border-color); background-color: var(--code-bg-color); font-family: var(--monospace-font); font-size: var(--monospace-font-size); border-radius: 0.25rem; padding: 0px 0.125rem; line-height: var(--monospace-line-height); }
.md-fences { margin-bottom: 18px; margin-top: 15px; padding: 8px 1em 6px; }
a { color: var(--link-color); text-decoration: none; }
.outline-item:hover { color: var(--header-color); }
#write div.md-toc-tooltip { background-color: var(--background-color); }
:root { --accented-background-color: #464B5D; --light-header-color: #a5a7bd; --select-text-bg-color: #295080; --accent-color: rgb(120, 124, 136); --dark-accent-color: #464B5D; --background-color: #0F111A; --font-color: #8F93A2; --header-color: #EEFFFF; --border-color: #232629; --link-color: #6699CC; --code-bg-color: #0C1420; --hover-bg-color: #050505; --control-text-color: var(--font-color); --side-bar-bg-color: var(--background-color); --control-text-hover-color: var(--header-color); --item-hover-text-color: var(--header-color); --item-hover-bg-color: var(--hover-bg-color); --bg-color: var(--background-color); --text-color: var(--font-color); --meta-content-color: var(--accent-color); --md-char-color: var(--accent-color); --window-border: 0px solid rgba(0,0,0,0); --active-file-bg-color: var(--hover-bg-color); --rawblock-edit-panel-bd: var(--code-background-color); }
.outline-item:hover { background-color: var(--hover-bg-color); }
h1, h2, h3, h4, h5, h6 { color: var(--light-header-color); }
mark { background: rgb(184, 184, 10); }
table tr:nth-child(2n), thead { background-color: rgb(20, 19, 19); }
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java collection 集合学习
collection
collection 是一个接口，所以不能够实例化，只能通过其子类
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创建Collection对象的方法：
1.Collection c = new ArrayList();此时，c即为一个Collection 实例化的一个对象
Arraylist
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1.添加对象成员：集合对象.add(需添加的对象);(add方法永远都会成功，只返回true)
2.清除所有对象：集合对象.clear();
3.清楚单个对象：集合对象.remove(指定的对象)；将指定的对象清除掉
4.判断集合是否含有元素：集合对象.inEmpty();返回true、false
5.判断集合中含有对象个数：集合对象.size()；返回集合中含有对象的个数
6.将一个a集合添加到另一个b集合当中:b.addAll(a);（允许重复对象的存在）
7.移除集合a中含有结合b内的所有元素：a.removeAll(b);(只要移除b内一个元素就返回true)
8.判断集合a中是否含有b的全部对象:a.containsAll(b);当含全部才返回true
9.求两个集合内对象的交集：retainAll()
eg: 前提集合a,集合b
a.retainAll(b)
交际赋值给Aa, 返回值 表示，集合a内的成员是否发生了变化
如果 a内成员含有 a ,b,c
b内成员含有 a,b,c,d
a.retainAll(b) 则a成员不会发生变化，返回值为false因为a内成员没有发生变化
10.将结合转换成数组形式：toArray(); 返回Object[]数组
eg: Object [] objes = a.toArray();（这个过程其实就是一个向上继承的过程）
如果想用对象本身的方法的话需要向下还原成其特定的类型
如String s = (String ) objes[x];
11.逐带（遍历）：a.iterator(); 返回类型：Iterator（返回一个新的对象）
Iterator : 1.下一个对像：next();
2.判断下一个对象是否为空：hasNext();
3.
List（特点，有序（可以定位访问）且可重复）
1.由于是collection的子类，所以具有collection接口拥有的所以方法
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1.返回第一次出现的指定的对象： indexOf（对象名）
2.返回最后一次出现的指定的对象： indexOf（对象名）
3.根据下标删除指定对象： a.remove(下标) 返回被删除的对象
4.获得指定下标的对象: a.get(下标)
5.将指定位置的对象更换： a.set（下标，新对象）
6.在指定位置添加对象： a.add(下标，对象) 会将后续的元素向后平移
（下标不能超过所容器的长度+1，既 最多可以在容器最后添加）
7.列表迭代器（特殊的是可以访问上一个对象元素） ：a.listIterator(); 返回一个ListIterator的对象实例
eg:ListIterator lit = new a.listIterator();
lit.previous() 这个是其特有的功能，作用是访问上一个对象元素
hasPrevious（） 判断是否存在对象元素
previous (一般没有实际用，因为指针默认指向首位)