[Chapter 4] 4.8 Relational Comparison Operators

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| Chapter 4 Expressions |

## 4.8 Relational Comparison Operators

The relational comparison operators in Java are used for less than (`<`), less than or equal to (`<=`), greater than or equal to (`>=`), greater than (`>`), and `instanceof` comparison operations. They may appear in a relational expression:

The relational comparison operators are equal in precedence and are evaluated from left to right. The `<`, `<=`, `>=`, and `>` operators are numerical comparison operators, while `instanceof` is a type comparison operator. All of these operators produce `boolean` values.

References Shift Operators; Order of Operations; Type 3

### Less-Than Operator <

The less-than operator < performs a comparison between its operands and returns a `boolean` value. It returns the pure value `true` if its left operand is less than its right operand; otherwise the operator returns the pure value `false`. The `<` operator may appear as part of a relational expression. The less-than operator never throws an exception.

The types of both operands of the less-than operator must be arithmetic types, or a compile-time error occurs. The `<` operator may perform type conversions on its operands:

- If either operand is of type `double`, then the other operand is converted to `double`.

- Otherwise, if either operand is of type `float`, the other operand is converted to `float`.

- Otherwise, if either operand is of type `long`, the other operand is converted to `long`.

- Otherwise, both operands are converted to `int`.

The comparison of any two arithmetic values produces `true` if the value of the left operand is less than the value of the right operand; otherwise the comparison produces `false`. The comparison of floating-point data is governed by the following additional rules:

- If either operand is not-a-number (NaN), the comparison produces `false`.

- Negative infinity is the most negative value. If the left operand is negative infinity, the comparison produces `true`, unless the right operand is also negative infinity, in which case the comparison produces `false`.

- Positive infinity is the most positive value. If the right operand is positive infinity, the comparison produces `true`, unless the left operand is also positive infinity, in which case the comparison produces `false`.

- Positive and negative zero are treated as equal, so `-0.0 < 0.0` produces `false`.

References Arithmetic Types

### Less-Than-Or-Equal-To Operator <=

The less-than-or-equal-to operator `<=` performs a comparison between its operands and returns a `boolean` value. It returns the pure value `true` if its left operand is less than or equal to its right operand; otherwise the operator returns the pure value `false`. The `<=` operator may appear as part of a relational expression. The less-than-or-equal-to operator never throws an exception.

The types of both operands of the less-than-or-equal-to operator must be arithmetic types, or a compile-time error occurs. The `<=` operator may perform type conversions on its operands:

- If either operand is of type `double`, then the other operand is converted to `double`.

- Otherwise, if either operand is of type `float`, the other operand is converted to `float`.

- Otherwise, if either operand is of type `long`, the other operand is converted to `long`.

- Otherwise, both operands are converted to `int`.

The comparison of any two arithmetic values produces `true` if the value of the left operand is less than or equal to the value of the right operand; otherwise the comparison produces `false`. The comparison of floating-point data is governed by the following additional rules:

- If either operand is not-a-number (NaN), the comparison produces `false`.

- Negative infinity is the most negative value. If the left operand is negative infinity, the comparison always produces `true`.

- Positive infinity is the most positive value. If the right operand is positive infinity, the comparison always produces `true`.

- Positive and negative zero are treated as equal, so `0.0 <= -0.0` produces `true`.

References Arithmetic Types

### Greater-Than-Or-Equal-To Operator >=

The greater-than-or-equal-to operator `>=` performs a comparison between its operands and returns a `boolean` value. It returns the pure value `true` if its left operand is greater than or equal to its right operand; otherwise the operator returns the pure value `false`. The `>=` operator may appear as part of a relational expression. The greater-than-or-equal-to operator never throws an exception.

The types of both operands of the greater-than-or-equal-to operator must be arithmetic types, or a compile-time error occurs. The `>=` operator may perform type conversions on its operands:

- If either operand is of type `double`, then the other operand is converted to `double`.

- Otherwise, if either operand is of type `float`, the other operand is converted to `float`.

- Otherwise, if either operand is of type `long`, the other operand is converted to `long`.

- Otherwise, both operands are converted to `int`.

The comparison of any two arithmetic values produces `true` if the value of the left operand is greater than or equal to the value of the right operand; otherwise the comparison produces `false`. The comparison of floating-point data is governed by the following additional rules:

- If either operand is not-a-number (NaN), the comparison produces `false`.

- Negative infinity is the most negative value. If the right operand is negative infinity, the comparison always produces `true`.

- Positive infinity is the most positive value. If the left operand is positive infinity, the comparison always produces `true`.

- Positive and negative zero are treated as equal, so `-0.0 >= 0.0` produces `true`.

References Arithmetic Types

### Greater-Than Operator >

The greater-than operator `>` performs a comparison between its operands and returns a `boolean` value. It returns the pure value `true` if its left operand is greater than its right operand; otherwise the operator returns the pure value `false`. The `>` operator may appear as part of a relational expression. The greater-than operator never throws an exception.

The types of both operands of the greater-than operator must be arithmetic types, or a compile-time error occurs. The `>` operator may perform type conversions on its operands:

- If either operand is of type `double`, then the other operand is converted to `double`.

- Otherwise, if either operand is of type `float`, the other operand is converted to `float`.

- Otherwise, if either operand is of type `long`, the other operand is converted to `long`.

- Otherwise, both operands are converted to `int`.

The comparison of any two arithmetic values produces `true` if the value of the left operand is greater than the value of the right operand; otherwise the comparison produces `false`. The comparison of floating-point data is governed by the following additional rules:

- If either operand is not-a-number (NaN), the comparison produces `false`.

- Negative infinity is the most negative value. If the right operand is negative infinity, the comparison produces `true`, unless the left operand is also negative infinity, in which case the comparison produces `false`.

- Positive infinity is the most positive value. If the left operand is positive infinity, the comparison produces `true`, unless the right operand is also positive infinity, in which case the comparison produces `false`.

- Positive and negative zero are treated as equal, so `0.0 > -0.0` produces `false`.

References Arithmetic Types

### The instanceof Operator

The `instanceof` operator performs a type comparison between its operands and returns a `boolean` value. It returns the pure value `true` if the object referred to by the left operand can be cast to the type specified as the right operand; otherwise the operator returns the pure value `false`. If the value of the left operand is `null`, the `instanceof` operator returns the pure value `false`. The `instanceof` operator may appear as part of a relational expression. The `instanceof` operator never throws an exception.

The type of the left operand of the `instanceof` operator must be a reference type, or a compile-time error occurs.

All objects inherit a method called `equals()` from the `Object` class. The `equals()` method defined in the `Object` class returns `true` if the two objects being compared are the same object. For some classes, it is more appropriate to override the `equals()` method so that it compares the contents of two objects. Before such a method can do the comparison, it should verify that the objects are instances of the same class by using `instanceof`. For example, let's suppose that you are defining a class to represent complex numbers. Since you want the `equals()` method to compare the contents of complex number objects, you define an `equals` method for the complex number class that looks like this:

    boolean equals (Object o) {
       if (o instanceof complexNumber)
           return o.real == this.real
               && o.imaginary == this.imaginary;
    }

The `instanceof` operator can also be used to find out if an object is an instance of a class that implements an interface. For example:

    if (o instanceof Runnable)
        (new Thread((Runnable)o).start;

References Casts; Class Types; Interface Types

Shift Operators |  | Equality Comparison Operators