数组和第一类对象[Java编程]

无论利用的数组属于什么范例,数组标识符实际都是指向真实对象的一个句柄.那些对象本身是在内存“堆”里成立的.堆对象既可“隐式”成立（即默许产生）,亦可“显式”成立（即明确指定,用一个new表达式）.堆对象的一部份（实际是我们能拜候的唯一字段或办法）是只读的length（长度）成员,它奉告我们那个数组对象里最多能包容多少元素.关于数组对象,“[]”语法是我们能采取的唯一另类拜候办法.
下面这个例子展示了对数组举行初始化的差别方法,以及若何将数组句柄分配给差别的数组对象.它也揭暴露对象数组和基本数据范例数组在利用办法上几近是完好一致的.唯一的差别在于对象数组包容的是句柄,而基本数据范例数组包容的是具体的数值（若在履行此程序时碰到艰难,请参考第3章的“赋值”小节）:

//: ArraySize.java
// Initialization & re-assignment of arrays
package c08;

class Weeble {} // A small mythical creature

public class ArraySize {
  public static void main(String[] args) {
    // Arrays of objects:
    Weeble[] a; // Null handle
    Weeble[] b = new Weeble[5]; // Null handles
    Weeble[] c = new Weeble[4];
    for(int i = 0; i < c.length; i++)
      c[i] = new Weeble();
    Weeble[] d = {
      new Weeble(), new Weeble(), new Weeble()
    };
    // Compile error: variable a not initialized:
    //!System.out.println("a.length=" + a.length);
    System.out.println("b.length = " + b.length);
    // The handles inside the array are 
    // automatically initialized to null:
    for(int i = 0; i < b.length; i++)
      System.out.println("b[" + i + "]=" + b[i]);
    System.out.println("c.length = " + c.length);
    System.out.println("d.length = " + d.length);
    a = d;
    System.out.println("a.length = " + a.length);
    // Java 1.1 initialization syntax:
    a = new Weeble[] {
      new Weeble(), new Weeble()
    };
    System.out.println("a.length = " + a.length);

    // Arrays of primitives:
    int[] e; // Null handle
    int[] f = new int[5];
    int[] g = new int[4];
    for(int i = 0; i < g.length; i++)
      g[i] = i*i;
    int[] h = { 11, 47, 93 };
    // Compile error: variable e not initialized:
    //!System.out.println("e.length=" + e.length);
    System.out.println("f.length = " + f.length);
    // The primitives inside the array are
    // automatically initialized to zero:
    for(int i = 0; i < f.length; i++)
      System.out.println("f[" + i + "]=" + f[i]);
    System.out.println("g.length = " + g.length);
    System.out.println("h.length = " + h.length);
    e = h;
    System.out.println("e.length = " + e.length);
    // Java 1.1 initialization syntax:
    e = new int[] { 1, 2 };
    System.out.println("e.length = " + e.length);
  }
} ///:~

b.length = 5
b[0]=null
b[1]=null
b[2]=null
b[3]=null
b[4]=null
c.length = 4
d.length = 3
a.length = 3
a.length = 2
f.length = 5
f[0]=0
f[1]=0
f[2]=0
f[3]=0
f[4]=0
g.length = 4
h.length = 3
e.length = 3
e.length = 2