String.md

String

两种新建方法，存储位置

通过new新建的存储在堆上

String heap1 = new String("heap");
不通过new新建的存在常量池

String constantArea1 = "constantArea";
编码验证

 private static void testStorLocation(){

 	//在堆上声明
 	String heap1 = new String("heap");
 	String heap2 = new String("heap");

 	//在常量池声明
 	String constantArea1 = "constantArea";
 	String constantArea2 = "constantArea";

 	//String重写过hashCode，String的值一样则hashCode一样
 	System.out.println(System.identityHashCode(heap1));
 	System.out.println(System.identityHashCode(heap2));
 	System.out.println(System.identityHashCode(constantArea1));
 	System.out.println(System.identityHashCode(constantArea2));
 }

 Begin test [testStorLocation]
 10568834  //new申请地址不同
 21029277
 24324022  //非new申请地址相同
 24324022

长度 Length()

length 等于Unicode字符的数量

String实际存储为final char[]类型，char类型为Unicode,长度为2个Byte. 关于Unicode：Unicode 只是一个符号集，它只规定了符号的二进制代码(它就是个取值，其他类似UTF-8是编码格式)，却没有规定这个二进制代码应该如何存储。更多相关Unicode请参考

	private static void length(){
		String test = "test1";

		System.out.println("Ori is " + test);
		System.out.println("Length  = " + test.length());


		String testChinese = "中文";
		System.out.println("Ori is " + testChinese);
		System.out.println("Length Chinese = " + testChinese.length());
	}

		Ori is test1
		Length  = 5
		Ori is 中文
		Length Chinese = 2

比较 equals() compareTo()

equals判断是否相等，compareTo还能判断大小。

 private static void equalsAndCompareTo() {
 	String test1 = "test1";
 	String test2 = "test2";
 	System.out.println("Ori test1 is " + test1);
 	System.out.println("Ori test2 is " + test2);

 	// equals 只判断是否相等， compareTo能判断大小，返回INT型
 	System.out.println("equls = " + test1.equals(test2));
 	System.out.println("compareTo = " + test1.compareTo(test2));
 }

 Ori test1 is test1
 Ori test2 is test2
 equls = false
 compareTo = -1

取字符 charAt()
大小写转换 toUpperCase() toLowerCase
连接 concat()
判断开头 startWith() endWith()
模式匹配(获取某个字符或字符串首次出现的位置) indexOf() lastIndexOf()
子串 substring()
修建左右空白 trim()
替换 replace() replaceAll()
拆分 split()

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