java | operator is for what?

Question

What is the output of this java code and why ?

 int a = 5 | 3 ;
 System.out.println(a);

Answer 1

It's called "bitwise OR".

5 | 3 in bits is equal to

0101
or
0011
----
0111

Before enums appered in java 5, it was a common pattern to make some constants equals to powers of 2 and use bitwise OR to express both properties. For example, let's assume that font can be BOLD, ITALIC and UNDERLINED. Then if you have constants:

public class FontStyle {
    final int BOLD = 1;
    final int ITALIC = 2;
    final int UNDERLINED = 4;

    private int fontStyle;

    public void setFontStyle(int style) {
       this.fontStyle = fontStyle;
    }

    public boolean hasStyle(int style) {
       return fontStyle & style == style;
    }
}

Then, if you want to create style BOLD and UNDERLINED - just do this:

FontStyle boldAndUnderlined = new FontStyle();
boldAndUnderlined.setFOntStyle(FontStyle.BOLD | FontStyle.UNDERLINED);