回顾JavaSE（2）-String（1）API构造方法

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温故而知新，在Android开发的道路上越走越远的同时，不能忘了JavaSE。

String，最常用的类，没有之一。

先看最好的教材，官方API文档。

```
public final class Stringextends Objectimplements Serializable, Comparable<String>, CharSequence
```
The String class represents character strings. All string literals in Java programs, such as"abc", are implemented as instances of this class.
Strings are constant; their values cannot be changed after they are created. String buffers support mutable strings. Because String objects are immutable they can be shared. For example:
```
     String str = "abc"; 
```
is equivalent to:
```
     char data[] = {'a', 'b', 'c'};     String str = new String(data);
```

String类概述

•字符串是由多个字符组成的一串数据(字符序列)

•字符串可以看成是字符数组

它的构造方法很多，我们重点看这几个：

构造方法：

•public String()

•public String(byte[] bytes)

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

•public String(char[] value)

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

•public String(String original)

先重点看它里面的length方法：

```
public int length()
```
Returns the length of this string. The length is equal to the number ofUnicode code units in the string.
Specified by:
length in interface CharSequence
Returns:
the length of the sequence of characters represented by this object.

是时候看一波源代码：

public class StringTest {/** * @param args * 权兴权意-20160919 * 字符串：多个字符组成的一串数据，也可以看做是字符数组 */public static void main(String[] args) {// TODO Auto-generated method stubString s1 = new String();System.out.println("s1:" + s1);System.out.println("s1.length():" + s1.length());System.out.println("--------------");byte[] b = {97,98,99,100};String s2 = new String(b);System.out.println("s2:" + s2);System.out.println("s2.length():" + s2.length());System.out.println("--------------");String s3 = new String(b,1,2);System.out.println("s3:" + s3);System.out.println("s3.length():" + s3.length());System.out.println("--------------");char[] c = {'a','b','c','d','权'};String s4 = new String(c);System.out.println("s4:" + s4);System.out.println("s4.length():" + s4.length());System.out.println("--------------");String s5 = new String(c,1,2);System.out.println("s5:" + s5);System.out.println("s5.length():" + s5.length());System.out.println("--------------");String s6 = new String("abcd");System.out.println("s6:" + s6);System.out.println("s6.length():" + s6.length());System.out.println("--------------");String s7 = "abcd";System.out.println("s7:" + s7);System.out.println("s7.length():" + s7.length());}}

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