一、理解 isEmpty()完全等同于string.length()==0 若String对象本身是NULL,即字符串对象的引用是空指针,那在使用String.isEmpty()方法时会提示NullPointerException。 二、两者的区别 isEmpty() (1)isEmpty()使用的前提是字符串对象已经被分配了内存空间,如果对象没有被分配空间而使用; (2)isEmpty()报空指针...
比较来自不同数据库的两个 bean 时出现此错误 java.lang.AssertionError: expected: null<null> but was: java.lang.String<null> at org.junit.Assert.fail(Assert.java:88) at org.junit.Assert.failNotEquals(Assert.java:834) at org.junit.Assert.assertEquals(Assert.java:118) at org.junit.Assert.ass...
packagecom.example.core.mydemo.json2;/*** int类型在接收null会报错,需要使用Java包装类型Integer*/publicclassIntegerNullTest {publicstaticvoidmain(String[] args) { Integer aaa=null;//output: total=100System.out.println("total=" +calc(aaa));//Exception in thread "main" java.lang.NullPointerExc...
2526哦,我明白了,意思就是Stringstring=null跟Stringstring;是一回事儿2728null是空对象""是空字符串29Strings=null;//null是未分配堆内存空间30Stringa;//分配了一个内存空间,没存入任何对象31Stringa="";//分配了一个内存空间,存了一个字符串对象32333435问题二:36Strings;和Strings=null;和Strings="a";有什...
给定如下所示的java代码,运行时会产生( )类型的异常。 String s=null; s.concat(“abc”);A.NullPointerExceptionB.
c:\>java TestNullOrEmpty value is null. value is blank but not null. value is " SuSouC" value is "hello me!" 比较String地址相等 package com; public class A { /** * @param args */ public static void main(String[] args)
* int类型在接收null会报错,需要使用Java包装类型Integer */ public class IntegerNullTest { public static void main(String[] args) { Integer aaa = null; //output: total=100 System.out.println("total=" + calc(aaa)); //Exception in thread "main" java.lang.NullPointerException ...
Sometimes my app produces an IllegalArgumentException error. Steps to Reproduce Unfortunately I don't have repro steps. It looks like a random thing. Any hints on what is causing this? Trace or Log Output Fatal Exception: java.lang.IllegalArgumentException: string == null at android.opengl.GLE...
IsNullOrEmpty(String) 指示指定的字符串是 null 还是空字符串(“)。 IsNullOrWhiteSpace(String) 指示指定的字符串是 null、空还是仅包含空格字符。 Join(Char, Object[]) 使用每个成员之间的指定分隔符连接对象数组的字符串表示形式。 Join(Char, ReadOnlySpan<Object>) 使用每个成员之间的指定分隔符连接对象范围...
最近在读《Thinking in Java》,看到这样一段话: Primitives that are fields in a class are automatically initialized to zero, as noted in the Everything Is an Object chapter. But the object references are initialized to null, and if you try to call methods for any of them, you’ll get an...