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Java String类

智云科技发布于 2023年4月29日评论关闭阅读(95)

目录

概述

字符串广泛应用 在 Java 编程中，在 Java 中字符串属于对象，Java 提供了 String 类来创建和操作字符串。

jdk中提供非常多的字符和字符串操作方法及构造方法，这里只介绍一些常用的方法和构造方法。完整的String类下的方法可以参考官方的API文档。

本地API文档下载：

在线API文档：

API文档截图：

对象创建

直接使用字面值

可以直接定义String类型的变量直接给其赋值一个字符串字面值

例： 

 <pre class="hljs nginx" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 0.75em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">String name = "愷龍";</pre>

使用构造方法

可以使用String中定义的构造方法来创建对象。String类下有非常多的构造方法，这里只介绍几个常用的。

String() 

 public String();

初始化新创建的字符串对象，使其表示空字符序列。

示例代码： 

 <pre class="prettyprint hljs typescript" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public static void main(String[] args) {
        //使用无参构造创建。字符串的内容为空 相当于 ""
        String s1 = new String();
    }</pre>

String(byte[] bytes) 

 String(byte[] bytes);

将数组转换为字符串。

示例代码： 

 <pre class="prettyprint hljs typescript" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public static void main(String[] args) {

        byte[] bytes = {68,74,84,85};
        String s = new String(bytes);
        System.out.println(s);//输出结果为DJTU,这里是将数字通过ASC码表转换为了字母
    }</pre>

结果：

String(byte[] bytes, int offset, int length)

通过使用平台的默认字符集解码指定的 byte 子数组，构造一个新的 String。

参数：

bytes：要解码为字符的 byte

offset： 要解码的第一个 byte 的索引

length： 要解码的 byte 数 的长度

示例代码： 

 <pre class="prettyprint hljs typescript" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public static void main(String[] args) {
        byte[] bytes = {68,74,84,85};
        String s = new String(bytes,0,2);
        System.out.println(s);//输出结果为DJ,从第0个开始长度为2个
        String s2 = new String(bytes,0,1);
        System.out.println(s2);//输出结果为D，从第0个开始长度为1个
    }</pre>

结果：

String(char[] value)

转换字符数组为字符串类

示例代码： 

 <pre class="prettyprint hljs typescript" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public static void main(String[] args) {
        char[] chars = {'D','J','T','U'};
        String s = new String(chars);
        System.out.println(s);//输出结果为DJTU
    }</pre>

结果：

String(char[] value, int offset, int count)

参数：

value – 作为字符源的数组。

offset – 初始偏移量。

count – 长度。

就是在数组value上选取一部分成为String对象。

示例代码： 

 <pre class="prettyprint hljs typescript" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public static void main(String[] args) {
        char[] chars = {'D','J','T','U'};
        String s = new String(chars,0,1);
        System.out.println(s);//输出结果为D
        String ss = new String(chars,0,2);
        System.out.println(s2);//输出结果为DJ
    }</pre>

结果：

Java String类

常用方法

方法

解释

String[] split(String regex)

把一个字符串按照指定的分隔符切割成多个字符串，把多个字符串放在一个字符串数组中返回

char[] toCharArray();

把一个字符串的内容转换成一个字符数组

byte[] getBytes();

把一个字符串的内容转换成一个byte数组

String substring(int index);

把某个字符串从index索引开始截取到最后

String substring(int begin,int end)

把某个字符串索引begin到索引end截取出来

boolean equals(Object anObject)

判断两个字符串的内容是否相同

split方法演示 

 <pre class="prettyprint hljs dart" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public static void main(String[] args) {
        String s = "DJTU,China,LiaoNing,DaLian";
        String[] strs = s.split(",");//以,分割
        for (int i = 0; i < strs.length; i++) {
            System.out.println(strs[i]);
        }
    }</pre>

结果：

toCharArray方法演示 

 <pre class="prettyprint hljs cs" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public static void main(String[] args) {
        String s = "DJTU";
        char[] chars = s.toCharArray();
        for (int i = 0; i < chars.length; i++) {
            System.out.println(chars[i]);
        }
    }</pre>

结果：

getBytes方法演示 

 <pre class="prettyprint hljs cs" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public static void main(String[] args) {
        String s = "DJTU";
        byte[] bytes = s.getBytes();//按照ASC码表转换为数字
        for (int i = 0; i < bytes.length; i++) {
            System.out.println(bytes[i]);
        }
    }</pre>

结果：

substring方法演示 

 <pre class="prettyprint hljs typescript" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public static void main(String[] args) {
        String s = "DJTU";
        String substring = s.substring(1);//从第[1]个开始截取
        System.out.println(substring);
    }</pre>

结果： 

 <pre class="prettyprint hljs typescript" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public static void main(String[] args) {
        String s = "DJTU";
        String substring = s.substring(1,2);//从第[1]个开始到第[2]个结束（不包含第[2]个）
        System.out.println(substring);
    }</pre>

equals方法演示 

 <pre class="prettyprint hljs typescript" style="padding: 0.5em; font-family: Menlo, Monaco, Consolas, "Courier New", monospace; color: rgb(68, 68, 68); border-radius: 4px; display: block; margin: 0px 0px 1.5em; font-size: 14px; line-height: 1.5em; word-break: break-all; overflow-wrap: break-word; white-space: pre; background-color: rgb(246, 246, 246); border: none; overflow-x: auto; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public static void main(String[] args) {
        String s = "DJTU";
        String s2 = "DJTU";
        String s3 = "DJTUD";
        boolean flag = s.equals(s2);
        boolean flag1 = s.equals(s3);
        System.out.println(flag);//输出true
        System.out.println(flag1);//输出false
    }</pre>

结果：

特点

  1. 一个字符串一旦创建其内容是永远不会变的
  2. 字符串效果上相当于是char[]字符数组，但是底层其实是byte[]字节数组
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文章来源：智云一二三科技

文章标题：Java String类

文章地址：https://www.zhihuclub.com/180322.shtml

关于作者: 智云科技

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