**
Related to "==" and equals ()
**
2019/03/30
(1) for string variables, ""Itself is more variable value (i.e., the first two objects of the
address)." The equals () "is the same string content Comparative
Example: String S1 =" 123 ";
String S2 =" 123 ";
String S3, S4;
new new String = S3 ( "123");
S4 = new new String ( "123");
S1s2; // false memory address is not the same two variables i.e. they point to different objects
s1.equals (s2) // true contents of the same two variables contained
(2) the StringBuffer the StringBuffer new new S1 = ( "A");
the StringBuffer the StringBuffer new new S2 = ( "A");
s1.equals (S2); // not be rewritten to false the StringBuffer equals () method, which is so
address comparison
(3) For non-string variables, "First address "and" the equals "is the comparison target memory
Example:
Class A {
A = OBJ1 new new A ();
A = obj2 new new A ();
OBJ1obj2; //false
obj.equls(obj2); //false
}
(4) more basic type only by comparison "==." The basic types with equals () comparing unable to compile
(5) Package Type basic types of "==" comparison address "the equals" Comparison Content
（6）String（字符串），StringBuffer（线程安全的可变字符串序列），StringBuilder（可变字符串序列）
例:
public class TestEquals {
public static void main(String[] args) {
String s1 = “123”;
String s2 = “123”;
String s3 = “abc”;
String s4 = new String(“123”);
String s5 = new String(“123”);
String s6 = new String(“abc”);
System.out.println(s1 == s2);// true
System.out.println(s1.equals(s2));// true
System.out.println(s1 == s3);// flase
System.out.println(s1.equals(s3));// flase
System.out.println(s4 == s5);// flase
System.out.println(s4.equals(s5));// true
System.out.println(s4 == s6);// flase
System.out.println(s4.equals(s6));// flase
System.out.println (== S1 S4); to false //
System.out.println (s1.equals (S4)); // to true
}
}
When s1, s2 to a string constant, the object is created in the constant pool only one object, so the two references are the same
s4, s5 create two objects. Thus when false s4 == s5.
(7) 特殊情况
class Value {
int i;
}
public class TestEquips {
public static void main(String[] args) {
Value v1 = new Value();
Value v2 = new Value();
v1.i = v2.i = 100;
System.out.println(v1.equals(v2));// flase
System.out.println(v1 == v2);// false
}
}
解释：上面的例子中类Value并没有覆盖Object中的equals方法（即equals方法比较地址），
而是继承了该方法，因此它就是被用来比较地址的，又v1和v2的所指向的对象不
相同
