java String s = null; & String s="";

<pre name="code" class="java">package com.net;

public class Test {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		
		String s1 = null;
		String s2 = new String();
		String s3 = "";
		String s4;
		
//		System.out.println(s1.equals("null"));
		
		System.out.println(s1);
		System.out.println("s1 == null:" + (s1 == null));
		
		System.out.println(s2);
		System.out.println("s2 == null:" + (s3 == null));
		System.out.println("s2.equals():" + (s2.equals("")));
		
		System.out.println(s3);
		System.out.println("s3 == null:" + (s3 == null));
		System.out.println("s3.equals():" + (s3.equals("")));
		
//		System.out.println(s4);
//		System.out.println("s4 == null:" + (s4 == null));
		
//		System.out.println(s1 + ":" + s2 + ":" + s3);

	}

}

输出：

null
s1 == null:true


s2 == null:false
s2.equals():true


s3 == null:false
s3.equals():true