Java 數(shù)組參數(shù)

Java數(shù)據(jù)類(lèi)型教程 - Java數(shù)組參數(shù)

數(shù)組參數(shù)

我們可以將數(shù)組作為參數(shù)傳遞給方法或構(gòu)造函數(shù)。

我們傳遞給該方法的數(shù)組的類(lèi)型必須是與形式參數(shù)類(lèi)型兼容的賦值。

以下代碼顯示了如何將Array作為方法參數(shù)傳遞。

public class Main {
  public static void main(String[] args) {
    int[] num = { 1, 2 };

    System.out.println("Before  swap");
    System.out.println("#1: " + num[0]);
    System.out.println("#2: " + num[1]);

    swap(num);

    System.out.println("After  swap");
    System.out.println("#1: " + num[0]);
    System.out.println("#2: " + num[1]);
  }
  public static void swap(int[] source) {
    if (source != null && source.length == 2) {
      // Swap the first and the second elements
      int temp = source[0];
      source[0] = source[1];
      source[1] = temp;
    }
  }
}

上面的代碼生成以下結(jié)果。

數(shù)組參數(shù)參考

因?yàn)閿?shù)組是一個(gè)對(duì)象，所以它的引用的副本被傳遞給一個(gè)方法。

如果方法更改數(shù)組參數(shù)，實(shí)際參數(shù)不受影響。

import java.util.Arrays;

public class Main {
  public static void main(String[] args) {
    int[] origNum = { 1, 2, 3 };
    System.out.println("Before method  call:" + Arrays.toString(origNum));

    // Pass the array to the method
    tryArrayChange(origNum);

    System.out.println("After method  call:" + Arrays.toString(origNum));
  }

  public static void tryArrayChange(int[] num) {
    System.out.println("Inside method-1:" + Arrays.toString(num));
    // Create and store a new int array in num
    num = new int[] { 10, 20 };

    System.out.println("Inside method?2:" + Arrays.toString(num));
  }
}

上面的代碼生成以下結(jié)果。

數(shù)組參數(shù)的元素

存儲(chǔ)在數(shù)組參數(shù)的元素中的值可以在方法中始終更改。

以下代碼顯示了如何更改方法中的數(shù)組參數(shù)的元素。

import java.util.Arrays;

public class Main {
  public static void main(String[] args) {
    int[] origNum = { 1, 2, 3 };
    String[] origNames = { "Java", "SQL" };
    System.out.println("Before method  call, origNum:"
        + Arrays.toString(origNum));
    System.out.println("Before method  call, origNames:"
        + Arrays.toString(origNames));

    // Call methods passing the arrays 
    tryElementChange(origNum);
    tryElementChange(origNames);

    System.out.println("After method  call, origNum:"
        + Arrays.toString(origNum));
    System.out.println("After method  call, origNames:"
        + Arrays.toString(origNames));
  }

  public static void tryElementChange(int[] num) {
    if (num != null && num.length > 0) {
      num[0] = -1;
    }
  }

  public static void tryElementChange(String[] names) {
    if (names != null && names.length > 0) {
      names[0] = "T";
    }
  }
}

上面的代碼生成以下結(jié)果。

例子

以下代碼顯示如何更改對(duì)象數(shù)組元素。

class Item {
  private double price;
  private String name;

  public Item(String name, double initialPrice) {
    this.name = name;
    this.price = initialPrice;
  }

  public double getPrice() {
    return this.price;
  }

  public void setPrice(double newPrice) {
    this.price = newPrice;
  }

  public String toString() {
    return "[" + this.name + ", " + this.price + "]";
  }
}

public class Main {
  public static void main(String[] args) {
    Item[] myItems = { new Item("Pen", 2.11), new Item("Pencil", 0.10) };
    System.out.println("Before method  call  #1:" + myItems[0]);
    System.out.println("Before method  call  #2:" + myItems[1]);

    // Call the method passing the array of Item
    tryStateChange(myItems);

    System.out.println("After method  call  #1:" + myItems[0]);
    System.out.println("After method  call  #2:" + myItems[1]);
  }

  public static void tryStateChange(Item[] allItems) {
    if (allItems != null && allItems.length > 0) {
      allItems[0].setPrice(0.38);
    }
  }
}

上面的代碼生成以下結(jié)果。