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;
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|
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getClass().getName() + '@' + Integer.toHexString(hashCode()), println(), print() .
/* # 10: equals(), hashCode, toString():
Student.java */
package chapt04;
public class Student {
private int id;
private String name;
private int age;
public Student(int id, String name, int age){
this. id = id;
this. name = name;
this. age = age;
}
public int getId() {
return id;
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (obj instanceof Student){ //warning
Student temp = (Student) obj;
return this. id == temp.id &&
name.equals(temp.name) &&
this. age == temp.age;
} else
return false;
}
public int hashCode() {
return (int)(31 * id + age
+ ((name == null)? 0: name.hashCode()));
}
public String toString() {
return getClass().getName()+"@name" +name
+ " id:" + id + " age:" + age;
}
}
31 * id + age , id=1 age=2, 33, , 63. .
equals() Student , , Student , id, name age , .
/* # 11: : SubStudent.java */
package chapt04;
public class SubStudent extends Student {
private int idFaculty;
public SubStudent (int id, String n, int a, int idf){
super (id, n, a);
this. idFaculty = idf;
}
}
/* # 12: equals() :
StudentEq.java */
package chapt04;
public class StudentEq {
public static void main(String[] args) {
Student p1 = new Student(71, "", 19);
Student p2 = new Student(71, "", 19);
SubStudent p3 =
new SubStudent(71, "", 19, 5);
System. out. println(p1.equals(p2));
System. out. println(p1.equals(p3));
System. out. println(p3.equals(p1));
}
}
:
True
True
True
equals() , , . .
|
|
|
, //warning equals() Student Class :
if (getClass() == obj.getClass())
:
True
False
False
equals() SubStudent , Student.
, , . , . () . Object protected - clone(), . clone() public . super. clone(), . , Cloneable. Cloneable (tagged) , , clone() Object . CloneNotSupportedException. , . C++ .
/* # 13: , : Student.java */
package chapt04;
public class Student implements Cloneable { /*
*/
private int id = 71;
public int getId() {
return id;
}
public void setId(int value) {
id = value;
}
public Object clone() { //
try {
return super. clone(); //
} catch (CloneNotSupportedException e) {
throw new AssertionError("!");
}
}
}
/* # 14: : DemoSimpleClone.java */
package chapt04;
public class DemoSimpleClone {
private static void changeId(Student p) {
p = (Student) p.clone(); //
p.setId(1000);
System. out. println("->id = " + p.getId());
}
public static void main(String[] args) {
Student ob = new Student();
System. out. println("id = " + ob.getId());
changeId(ob);
System. out. println("id = " + ob.getId());
}
}
:
id = 71
->id = 1000
id = 71
clone(), :
id = 71
->id = 1000
id = 1000
, (immutable) . , . , . .
/* # 15: : Student.java */
package chapt04;
import java.util.ArrayList;
public class Student implements Cloneable {
private int id = 71;
private ArrayList<Mark> lm = new ArrayList<Mark>();
public int getId() {
return id;
}
public void setId(int id) {
this. id = id;
}
public ArrayList<Mark> getMark() {
return lm;
}
public void setMark(ArrayList<Mark> lm) {
|
|
|
this. lm = lm;
}
public Object clone() {
try {
Student copy =(Student) super. clone();
copy.lm = (ArrayList<Mark>)lm.clone();
return copy;
} catch (CloneNotSupportedException e) {
throw new AssertionError(
" Cloneable!");
}
}
}
, Cloneable clone(). , . , , . final .
new, , . , , . , , , , , , . . , System.gc() Runtime.getRuntime().gc(), , . System.runFinalization() finalize() .
. , . : try-finally finalization. try-finally , . finalization . -
finalize() , JVM. , . , . finalize(), , , .
finalize() :
protected void finalize(){
//
}
protected finalize() , . finalize() , , , , finalize() , . ! .
/* # 16: Manager finalization: Manager.java */
package chapt04;
class Manager {
private int id;
public Manager(int value) {
id = value;
}
protected void finalize() throws Throwable {
try {
//
System. out. println(" , id=" + id);
|
|
|
} finally {
super. finalize();
}
}
}
package chapt04;
public class FinalizeDemo {
public static void main(String[] args) {
Manager d1 = new Manager(1);
d1 = null;
Manager d2 = new Manager(2);
Object d3 = d2; //1
//Object d3 = new Manager (3); //2
d2 = d1;
System.gc(); // " "
}
}
System.gc() .
, id=1
1 2, gc() .
, id=1
, id=2
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