java對象數組，java數組

java對象數組，java數組

java對象數組與普通數組有點不一樣其實最底層的原理是一樣的我們使用對象數組一定要記得創建立對象不然會報null 指標異常，

我已經遇到了兩次了，每次都浪費 了很長時間現在貼個初始化過程大家看看看好了下面一定要記得new對象不要只在前面new數組

public class Student
{

 private String username;
 private int num;

 public Student(String username, int num)
 {
  this.username = username;
  this.num = num;
 }

 public static void main(String[] args)
 {
  Student s[] = new Student[10];
  for (int i = 0; i < s.length; i++)
  {
   s[i] = new Student(i + "", i);
   System.out.println(s[i]);
  }

 }

 public String getUsername()
 {
  return username;
 }

 public void setUsername(String username)
 {
  this.username = username;
 }

 public int getNum()
 {
  return num;
 }

 public void setNum(int num)
 {
  this.num = num;
 }

 @Override
 public String toString()
 {
  return this.num + " " + this.username;
 }

}

對於Java中的對象數組

首先：Data []d=new Data[3]; 建立一個對象數組， 數組中有3個Data對象 已經初始化為null 但是沒有執行個體化
d[i]=new Data(); 的作用是執行個體化

java.lang.NullPointerException 的原因是 沒有執行個體化 就調用getData()方法
 
java 對象數組定義

public class Student
{

private String username;
private int num;

public Student(String username, int num)
{
this.username = username;
this.num = num;
}

public static void main(String[] args)
{
Student s[] = new Student[10];
for (int i = 0; i < s.length; i++)
{
s[i] = new Student(i + "", i);
System.out.println(s[i]);
}

}

public String getUsername()
{
return username;
}

public void setUsername(String username)
{
this.username = username;
}

public int getNum()
{
return num;
}

public void setNum(int num)
{
this.num = num;
}

@Override
public String toString()
{
return this.num + " " + this.username;
}

}