java中Student s1=new Student(); s2=s1; s3=s2; s4=s3;创建了几个对象？

　　public class Test {
　　public static void main(String[] args) {
　　String s1="Welcome to java";
　　String s2=s1;
　　String s3=new String("Welcome to java");
　　String s4=s3.intern();
　　
　　System.out.println("s1=s2:" + (s1==s2));
　　System.out.println("s2=s3:" + (s2==s3));
　　System.out.println("s1.equals（s2）:" + s1.equals(s2));
　　System.out.println("s2.equals（s3）:" + s2.equals(s3));
　　System.out.println("s1.compareTo（s2）:" + s1.compareTo(s2));
　　System.out.println("s2.compareTo（s3） :" + s2.compareTo(s3));
　　System.out.println("s1==s4:" + (s1==s4));
　　System.out.println("s1.charAt(0) :" + s1.charAt(0) );
　　System.out.println("s1.indexOf('j') :" + s1.indexOf('j') );
　　System.out.println("s1.indexOf('to'):" + s1.indexOf("to"));
　　System.out.println("s1.lastindexOf('j') :" + s1.lastIndexOf("j"));
　　System.out.println("s1.lastindexOf(\"o\",15):" + s1.lastIndexOf("o",15));
　　System.out.println("s1.length():" + s1.length());
　　System.out.println("s1.subString(5):" + s1.substring(5));
　　System.out.println("s1.SubString(5,11):" + s1.substring(5,11));
　　System.out.println("s1.startsWith(\"wel\"):" + s1.startsWith("wel"));
　　System.out.println("s1.endsWith(\"java\"):" + s1.endsWith("java"));
　　System.out.println("s1.toLowerCase():" + s1.toLowerCase());
　　System.out.println("s1.toUpperCase():" + s1.toUpperCase());
　　System.out.println("\" Welcome \".trim():" + " Welcome ".trim());
　　System.out.println("s1.replace('o','T'):" + s1.replace('o','T'));
　　System.out.println("s1.replaceAll(\"o\",\"T\"):" + s1.replaceAll("o","T"));
　　System.out.println("s1.replaceFirst(\"o\",\"T\"):" + s1.replaceFirst("o","T"));
　　System.out.println("s1.toCharArray():" + s1.toCharArray());
　　}
　　}