String面试题

1.String.intern()方法返回常量池中和String对象的值相同的常量的引用,如果常量池中没有该常量,则把该String对象的值加入常量池

		String s1 = "programming";
		String s2 = new String("programming");
		String s3 = "program";
		String s4 = "ming";
		String s5 = "program" + "ming";
		String s6 = s3 + s4; // s6指向新的对象
		System.out.println(s1 == s2); // false
		System.out.println(s1 == s5); // true
		System.out.println(s1 == s6); // false
		System.out.println(s1 == s6.intern()); // true
		System.out.println(s2 == s2.intern()); // false
		System.out.println(s1 == s2.intern()); // true
		System.out.println(s6 == s6.intern()); // false

          String str1 = "str";
          String str2 = "ing";
          String str3 = "str" + "ing";//常量池中的对象
          String str4 = str1 + str2; //在堆上创建的新的对象      
          String str5 = "string";//常量池中的对象
          System.out.println(str3 == str4);//false
          System.out.println(str3 == str5);//true
          System.out.println(str4 == str5);//false