Geek asks and answers

Return false from Equals methods without overriding

Write the TestEquals classmain class method to Puzzle3print false.

Note. You cannot override the equals method of the TestEquals class.

public class Puzzle3 {
    public static void main(String[] args) {
        TestEquals testEquals = new TestEquals();
        System.out.println(testEquals.equals(testEquals));
    }
}

I did not find a way to achieve this, please share your comments

-2
source share
3 answers

You cannot override the equals method, but there is no reason why you cannot overload the equals method.

The Object.equals method has a prototype:

public boolean equals(Object o) { ... }

, TestEquals. , . , . TestEquals:

public boolean equals(TestEquals o) { return false; }

.

+4

class TestEquals {
    // a common mistake which doesn't override equals(Object)
    public boolean equals(TestEquals te) { 
          return false;
    }
}
+3

The following will print false :)

import java.io.File;
import java.io.FileNotFoundException;
import java.io.OutputStream;
import java.io.PrintStream;
import java.io.UnsupportedEncodingException;

public class TestEquals {

  public static void main(String[] args) {
    TestEquals testEquals = new TestEquals();
    System.out.println(testEquals.equals(testEquals));
  }

  static {
    System.setOut(new CustomPrintStream(new PrintStream(System.out)));
  }

  public static class CustomPrintStream extends PrintStream {

    /**
     * This does the trick.
     */
    @Override
      public void println(boolean x) {
      super.println(!x);
    }

    public CustomPrintStream(File file, String csn) throws FileNotFoundException, UnsupportedEncodingException {
      super(file, csn);
    }

    public CustomPrintStream(File file) throws FileNotFoundException {
      super(file);
    }

    public CustomPrintStream(OutputStream out, boolean autoFlush, String encoding)
      throws UnsupportedEncodingException {
      super(out, autoFlush, encoding);
    }

    public CustomPrintStream(OutputStream out, boolean autoFlush) {
      super(out, autoFlush);
    }

    public CustomPrintStream(OutputStream out) {
      super(out);
    }

    public CustomPrintStream(String fileName, String csn) throws FileNotFoundException,
                                                                 UnsupportedEncodingException {
      super(fileName, csn);
    }

    public CustomPrintStream(String fileName) throws FileNotFoundException {
      super(fileName);
    }
  }
}
+3
source

More articles:


All Articles