String.intern 示例

		//字符串常量池
		String str1 = "str";
		String str2 = "ing";
		String str3 = "str" + "ing";
		String str4 = str1 + str2;
		System.out.println(str3 == str4);	//false
		String str5 = "string";
		System.out.println(str3 == str5);	//true
		
		// 将两个常量用+连接对s进行初始化 
		String s = A + B;	// 将两个常量用+连接对s进行初始化  等同于：String s="ab"+"cd";
		String t = "abcd";   
		System.out.println(s == t);   //true
		String _s = _A + _B;   
		String _t = "abcd";   
		System.out.println(_s == _t);  //false 

		//String.intern
		String s1 = new String("计算机");
		String s2 = s1.intern();
		String s3 = "计算机";
		System.out.println("s1 == s2? " + (s1 == s2));	//false
		System.out.println("s3 == s2? " + (s3 == s2));	//true
		
		String hello = "Hello", lo = "lo";
		System.out.print((hello == "Hello") + " ");
		System.out.print((hello == ("Hel"+"lo")) + " ");
		String _hello = "Hel"+lo;
		System.out.print((hello == _hello) + " ");
		System.out.println(hello == _hello.intern());	//true true false true
		
		//jdk1.7以后字符串常量池不在永久代中，而在堆中，String.intern会不会拷贝字符串到常量池中，
		//而是在常量池中保存指向堆中intern对象的引用
		String str11 = new String("hello");
		str11 = str11 + "world";
		str11.intern();
		String str12 = "helloworld";
		System.out.println(str11 == str12);	//true
		
		String str21 = new String("how");
		str21 = str21 + "areyou";
		String str22 = "howareyou";
		str21.intern();
		System.out.println(str21 == str22);	//false