equals

在Scala中你只需要使用==就可以判断字符串相等，而不需要像Java一样需要使用的equals方法来判断。 scala> val s1 = "hello" s1: String = hello scala> val s2 = "hello" s2: String = hello scala> val s3 = "h" + "ello" s3: String = hello scala> s1 == s2 res4: Boolean = true scala> s1 == s3 res5: Boolean = true 使用==判断字符串相等的好处是，可以避免空指针异常。即==左边的字符串是空，也可以正常判断。 scala> val s4 = null s4: Null = null scala> s4 == s3 res6: Boolean = false scala> s3 == s4 res7: Boolean = false 忽略大小写来比较两个字符串是否一致，有两个方法：一个是把两个字符串都转化为大写或者小写再比较，另一个是直接使用 equalsIgnoreCase 方法。 scala> val s1 = "hello" s1: String = hello scala> val s2 = "Hello" s2: String = Hello scala> s1

Object类位于java.lang包中，java.lang包包含着Java最基础和核心的类，在编译时会自动导入。Object类没有定义属性，一共有13个方法，具体的类定义结构如下图： 1.类构造器public Object(); 大部分情况下 ，Java中通过形如 new A(args..)形式创建一个属于该类型的对象。其中A即是类名，A(args..)即此类定义中相对应的构造函数。通过此种形式创建的对象都是通过类中的构造函数完成。为体现此特性，Java中规定：在类定义过程中，对于未定义构造函数的类，默认会有一个无参数的构造函数，作为所有类的基类，Object类自然要反映出此特性，在源码中，未给出Object类构造函数定义，但实际上，此构造函数是存在的。 当然，并不是所有的类都是通过此种方式去构建，也自然的， 并不是所有的类构造函数都是public。 2.private static native void registerNatives(); registerNatives函数前面有native关键字修饰，Java中，用native关键字修饰的函数表明该方法的实现并不是在Java中去完成，而是由C/C++去完成，并被编译成了.dll，由Java去调用。方法的具体实现体在dll文件中，对于不同平台，其具体实现应该有所不同。用native修饰，即表示操作系统，需要提供此方法

i have a class whose equality is based on 2 fields such that if either one is equal then the objects of this type are considered equal. how can i write a hashCode() function for such an equals() so that the general contract of hashCode being equal when equals returns true is preserved? public class MyClass { int id; String name; public boolean equals(Object o) { if (!(o instanceof MyClass)) return false; MyClass other = (MyClass) o; if (other.id == this.id || other.name == this.name) return true; return false; } } how do i write a hashCode() function for this class? and i want to avoid the

I'm having a problem with getting an ArrayList to correctly use an overriden equals. the problem is that I'm trying to use the equals to only test for a single key field, and using ArrayList.contains() to test for the existence of an object with the correct field. Here is an example public class TestClass { private static class InnerClass{ private final String testKey; //data and such InnerClass(String testKey, int dataStuff) { this.testKey =testKey; //etc } @Override public boolean equals (Object in) { System.out.println("reached here"); if(in == null) { return false; }else if( in instanceof

I just ran into a problem caused by Java's java.awt.geom.Area#equals(Area) method. The problem can be simplified to the following unit test: @org.junit.Test public void testEquals() { java.awt.geom.Area a = new java.awt.geom.Area(); java.awt.geom.Area b = new java.awt.geom.Area(); assertTrue(a.equals(b)); // -> true java.lang.Object o = b; assertTrue(a.equals(o)); // -> false } After some head scratching and debugging, I finally saw in the JDK source, that the signature of the equals method in Area looks like this: public boolean equals(Area other) Note that it does not @Override the normal

This question already has answers here : Javascript a=b=c statements (6 answers) I saw this code somewhere, but what does it mean? (all a, b, c are defined previously) var a = b = c; It quickly assigns multiple variables to a single value. In your example, a and b are now equal set to the value of c . It's also often used for a mass assign of null to clean up. a = b = c = d = null; Assign c to b. Assign b to a. So if I say var a = b = 1; >>> var a = b = 1; undefined >>> a 1 >>> b 1 This means a , b and c are the same reference. For example: var c = {hello: "world"}; var a = b = c; // now all