Java——return在构造函数的作用

最新推荐文章于 2025-07-04 21:22:53 发布

原创最新推荐文章于 2025-07-04 21:22:53 发布 · 3.2k 阅读

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本文探讨了构造函数中使用return的特殊行为，指出其只能终止构造过程而不会影响对象创建。并通过String类和Color类的构造函数示例，展示了如何通过异常处理确保构造参数的有效性。

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构造函数可以使用return来结束函数。

摘自String.class

    /**
     * Package private constructor. Trailing Void argument is there for
     * disambiguating it against other (public) constructors.
     *
     * Stores the char[] value into a byte[] that each byte represents
     * the8 low-order bits of the corresponding character, if the char[]
     * contains only latin1 character. Or a byte[] that stores all
     * characters in their byte sequences defined by the {@code StringUTF16}.
     */
    String(char[] value, int off, int len, Void sig) {
        if (len == 0) {
            this.value = "".value;
            this.coder = "".coder;
            return;
        }
        if (COMPACT_STRINGS) {
            byte[] val = StringUTF16.compress(value, off, len);
            if (val != null) {
                this.value = val;
                this.coder = LATIN1;
                return;
            }
        }
        this.coder = UTF16;
        this.value = StringUTF16.toBytes(value, off, len);
    }

在构造函数里使用了某些不一定能成功的操作，然后想在对这个类进行new操作的时候返回NULL。不过在构造函数里return以后，只是构造函数后面的步骤不走了，但new操作仍然成功。

不一定成功的操作，可以进行抛出异常。

摘自Color.class

    /**
     * Creates an sRGB color with the specified red, green, blue, and alpha
     * values in the range (0 - 255).
     *
     * @throws IllegalArgumentException if {@code r}, {@code g},
     *        {@code b} or {@code a} are outside of the range
     *        0 to 255, inclusive
     * @param r the red component
     * @param g the green component
     * @param b the blue component
     * @param a the alpha component
     * @see #getRed
     * @see #getGreen
     * @see #getBlue
     * @see #getAlpha
     * @see #getRGB
     */
    @ConstructorProperties({"red", "green", "blue", "alpha"})
    public Color(int r, int g, int b, int a) {
        value = ((a & 0xFF) << 24) |
                ((r & 0xFF) << 16) |
                ((g & 0xFF) << 8)  |
                ((b & 0xFF) << 0);
        testColorValueRange(r,g,b,a);
    }

    /**
     * Checks the color integer components supplied for validity.
     * Throws an {@link IllegalArgumentException} if the value is out of
     * range.
     * @param r the Red component
     * @param g the Green component
     * @param b the Blue component
     **/
    private static void testColorValueRange(int r, int g, int b, int a) {
        boolean rangeError = false;
        String badComponentString = "";

        if ( a < 0 || a > 255) {
            rangeError = true;
            badComponentString = badComponentString + " Alpha";
        }
        if ( r < 0 || r > 255) {
            rangeError = true;
            badComponentString = badComponentString + " Red";
        }
        if ( g < 0 || g > 255) {
            rangeError = true;
            badComponentString = badComponentString + " Green";
        }
        if ( b < 0 || b > 255) {
            rangeError = true;
            badComponentString = badComponentString + " Blue";
        }
        if ( rangeError == true ) {
        throw new IllegalArgumentException("Color parameter outside of expected range:"
                                           + badComponentString);
        }
    }

或者new成功后再进行一次判断。