假设s1，s2，s3.和s4是四个字符串，如下给出其值：
String s1 = “Welcome to java”；
String s2 = s1;
String s3 = new String(“Welcome to java”);
String s4 = “Welcome to java”;

假设s1，s2，s3.和s4是四个字符串，如下给出其值：
String s1 = “Welcome to java”；
String s2 = s1;
String s3 = new String(“Welcome to java”);
String s4 = “Welcome to java”;