接口和抽象類的定義方式舉例說明

鳳舞天煌 2007-05-30

展開全文

接口定義
關(guān)于java的接口定義方式，以下三種情況下可以采用接口定義方式：
1.    接口中聲明的變量全部為final 和static類型的，并且這個接口的作用在于定義一些值不能改變的變量。
舉個例子：
public interface ObjectConstants{
public static final String SPACE = new String(" ");
public static final char FORMFEED = ‘\f‘;
}
2.    接口中只定義可供實現(xiàn)的抽象方法
EventListener.java
    public interface EventListener {
    public void handleEvent(Event evt);
    }
Runnable.java
package java.lang;
    public interface Runnable {
    public abstract void run();
    }
3.    還有一種方式是上述兩種方式的組合，如非必要一般會將這樣一個接口定義拆分成兩個接口定義
抽象類的定義
1.    如果一個類包含一個接口但是不完全實現(xiàn)接口定義的方法，那么該類必須定義成abstract型
例如InputStream.java類的定義方式：
package java.io;
public abstract class InputStream implements Closeable {
    // SKIP_BUFFER_SIZE is used to determine the size of skipBuffer
    private static final int SKIP_BUFFER_SIZE = 2048;
    // skipBuffer is initialized in skip(long), if needed.
    private static byte[] skipBuffer;
    public abstract int read() throws IOException;


    public int read(byte b[]) throws IOException {
    return read(b, 0, b.length);
    }
    public int read(byte b[], int off, int len) throws IOException {
    if (b == null) {
        throw new NullPointerException();
    } else if ((off < 0) || (off > b.length) || (len < 0) ||
           ((off + len) > b.length) || ((off + len) < 0)) {
        throw new IndexOutOfBoundsException();
    } else if (len == 0) {
        return 0;
    }
    int c = read();
    if (c == -1) {
        return -1;
    }
    b[off] = (byte)c;
    int i = 1;
    try {
        for (; i < len ; i++) {
        c = read();
        if (c == -1) {
            break;
        }
        if (b != null) {
            b[off + i] = (byte)c;
        }
        }
    } catch (IOException ee) {
    }
    return i;
    }
public long skip(long n) throws IOException {
    long remaining = n;
    int nr;
    if (skipBuffer == null)
        skipBuffer = new byte[SKIP_BUFFER_SIZE];
    byte[] localSkipBuffer = skipBuffer;
    if (n <= 0) {
        return 0;
    }
    while (remaining > 0) {
        nr = read(localSkipBuffer, 0,
              (int) Math.min(SKIP_BUFFER_SIZE, remaining));
        if (nr < 0) {
        break;
        }
   remaining -= nr;
    }
    return n - remaining;
    }
    public int available() throws IOException {
    return 0;
    }
    public void close() throws IOException {}
    public synchronized void mark(int readlimit) {}
    public synchronized void reset() throws IOException {
    throw new IOException("mark/reset not supported");
    }
    public boolean markSupported() {
    return false;
    }
}
2.    抽象類的方法體中只定義抽象的方法，例如AbstractMethodError.java
    package java.lang;
    public class AbstractMethodError extends IncompatibleClassChangeError {
    public AbstractMethodError() {
    super();}
    public AbstractMethodError(String s) {
    super(s); }
}