08. 数组初始化

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FengXueke 10月 18, 2022
post08

数组初始化

  • 数组对象的赋值
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package com.isflee.c04_5_1_arrays;

//: Arrays.java
// Arrays of primitives.
public class Arrays {
    public static void main(String[] args) {
        int[] a1 = { 1, 2, 3, 4, 5 };
        int[] a2;
        //复制一个a1的句柄给未初始化的a2。 其实就是对数组对象进行赋值
        a2 = a1;
        for(int i = 0; i < a2.length; i++)
            a2[i]++;
        for(int i = 0; i < a1.length; i++)
            prt("a1[" + i + "] = " + a1[i]); }
    static void prt(String s) {
        System.out.println(s);
    }
} ///:~
  • 不同类型的数组成员的初始化

1.基本数据类型的数组, 成员不进行赋值时会被自动初始化成对应基本数据类型的默认值

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package com.isflee.c04_5_3_array_new;

import java.util.Random;

//: ArrayNew.java
// Creating arrays with new. import java.util.*;
public class ArrayNew {
    static Random rand = new Random();
    static int pRand(int mod) {
        return Math.abs(rand.nextInt()) % mod + 1;
    }
    public static void main(String[] args) {
        int[] a;
        //数据的类型是是基本数据类型
        a = new int[pRand(20)];
        prt("length of a = " + a.length);
        for(int i = 0; i < a.length; i++)
            //未对数组成员进行赋值(初始化)操作, 数组成员的值则使用默认值
            prt("a[" + i + "] = " + a[i]);
    }
    static void prt(String s) { System.out.println(s);
    }
} ///:~

2.非基本数据类型的数组, 成员必须进行初始化(创建对象), 否则会报错

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package com.isflee.c04_5_2_array_class_obj;

import java.util.Random;

//: ArrayClassObj.java
// Creating an array of non-primitive objects. import java.util.*;
public class ArrayClassObj {
    static Random rand = new Random();
    static int pRand(int mod) {
        return Math.abs(rand.nextInt()) % mod + 1;
    }
    public static void main(String[] args) {
        //数据的类型是Integer对象
        Integer[] a = new Integer[pRand(20)];
        prt("length of a = " + a.length);
        for(int i = 0; i < a.length; i++) {
            //对数组成员进行了初始化
            a[i] = new Integer(pRand(500));
            prt("a[" + i + "] = " + a[i]);
        }
    }
    static void prt(String s) {
        System.out.println(s);
    }
} ///:~

3.高级用法, 将数组的类型定义为Object(根类), 这种定义比较灵活且有用.

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package com.isflee.c04_var_args;

//: VarArgs.java
// Using the Java 1.1 array syntax to create // variable argument lists
class A { int i; }
public class VarArgs {
    static void f(Object[] x) {
    for(int i = 0; i < x.length; i++)
        System.out.println(x[i]);
}
    public static void main(String[] args) {
        f(new Object[] {
                new Integer(47), new VarArgs(),
                new Float(3.14), new Double(11.11) });
        f(new Object[] {"one", "two", "three" });
        f(new Object[] {new A(), new A(), new A()});
    }
} ///:~