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我们首先来看下面几个示例： import java.util.*; public class Test { public static void main(String []args) { String s1 = new String(); String s2 = ""; String s3 = null; String s4; if(s1 == null) { System.out.println("s1_1"); } if(s1.isEmpty())

Given a positive integer n, find the number ofnon-negativeintegers less than or equal to n, whose binary representations do NOT containconsecutive ones. Example 1: Input: 5 Output: 5 Explanation...

Given a string representing an expression of fraction addition and subtraction, you need to return the calculation result in string format. The final result should beirreducible fraction. If your fin...

1、获取字符串长度：length（） 2、获取字符串第i个位置的字符：charAt（i） 3、获取指定字符或者字符串的位置： indexOf（ch）返回的是第一次出现位置的索引 无指定字符或字符串返回-1 indexOf（ch，fromIndex）返回fromIndex之前第一次出现的位置索引 lastIndexOf（ch）返回的是最后一次出现的位置索引 lastIndexOd（...