Simple Examples

General Information

Simple Program Structure

Access.java

Static Methods

• The static method

        Integer.parseInt("0", 10)           returns 0
        Integer.parseInt("473", 10)         returns 473
        Integer.parseInt("-0", 10)          returns 0
        Integer.parseInt("-FF", 16)         returns -255
        Integer.parseInt("1100110", 2)      returns 102
        Integer.parseInt("2147483647", 10)  returns 2147483647
        Integer.parseInt("-2147483648", 10) returns -2147483648
        Integer.parseInt("2147483648", 10)  throws a NumberFormatException
        Integer.parseInt("99", 8)           throws a NumberFormatException
        Integer.parseInt(" 473", 10)        throws a NumberFormatException
        Integer.parseInt("473", 999)        throws a NumberFormatException
        Integer.parseInt("Kona", 10)        throws a NumberFormatException
        Integer.parseInt("Kona", 27)        returns 411787
         

• The related static method

        Double.parseDouble("0")           returns 0.0
        Double.parseDouble("-NaN")           returns 0.0
        

  See also , and . And the constructors , and .

• The static method

        String x = Integer.toString (i, 17);   // convert to base 17
        

• The Java class

  java.lang.Math examples: Examples.java output

• The Java class

  in, out, err, exit, arraycopy

        static byte [] slice (byte [] a, int offset, int length) {
           byte [] r = new byte [length];
           System.arraycopy (a, offset, r, 0, length);
           return r;
        }
        

• Create temporary files:

        final File temp = File.createTempFile("prefix-", ".suffix");
        temp.deleteOnExit();
        

• The Java class. Not to be confused with the class in package java.lang.reflect.

        String[] strs = {"dog", "pig", "cat"};
        Arrays.sort (strs);
  
        int[] ints = {9, 5, 1, 7};
        Arrays.sort (ints);
        

Input and Output

Java programs doing simple IO using the Java IO package .

• Read.java
• CopyFile.java
• CopyTextFile.java
• DataOut.java and DataIn.java

Other Idioms

• The Java class

        Process p = Runtime.getRuntime().exec ("ls -l");
        

  Note that these have to be executable programs not shell "psuedo" commands.

• The class

  StringFest.java

  toString conversion Binary operation + converts one, if any, non string argument (either one) to a string before concatenation. Note that println is overloaded it prints int values, String objects, etc. Other objects are converted by using the toString method inherited by all objects.

• Formatting!? Formatting numbers has lots of complexities.
  • The Java.lang.Integer method toString() coverts to base 2 through 36. For example,

    	    Integer.toString(n, 16).toUpperCase()
                

    might yield 1D2F. There are also the static methods toBinaryString(), toOctalString(), and toHexString().

  • padding, justifying, digits right of the decimal points!? Requires classes, in particular instantiation of the class . Squares.java
  • No way to align (right justify) strings.
  • Rounding decimal numbers. Requires classes, in particular instantiation of class DecimalFormat. DecimalFormat uses half-even rounding (BigDecimal.ROUND_HALF_EVEN) for formatting. Round.java