String 問題依然犯錯

String s1="ab";
String s2="a"+"b";  //被編譯器優化爲 "ab"
String s3="a";
String s4="b";
String s5=s3+s4;   //被建立在堆裏面
System.out.println(s5==s2); //false

String s1=」aa」; 
String s2=s1.intern(); 
System.out.print(s1==s2);//返回true