Java Programming Tutorials

Java programming tutorials with many code examples!

Java Util Map replace(key, value)

java.util.Map.replace(key, value)

The method Map.replace(key, value) associates the given value with the given key only when the map already contains such key.

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Java Util Map.putIfAbsent(key, value)

java.util.Map.putIfAbsent(key, value)

The method Map.putIfAbsent(key, value) associates the given key with the given value if there is no such association or the current value in map is null. Returns null or the previous value.

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Java Time Clock Tutorial

The java.time.Clock class provides access to the current instant, date and time using a time-zone. These are the main properties of the class:

  • Use of the Clock class is optional, because all key date-time classes have a now() factory method that uses the system clock in the default time zone.
  • Use Dependency Injection framework to provide Clock implementations.

The class declaration is:

public abstract class Clock
       extends Object

Methods inheritance

Objects of this class inherit methods from the following classes:

  • java.lang.Object

Methods of java.time.Clock:

  • boolean equals(Object obj)
    Checks if this clock is equal to another clock.
  • static Clock fixed(Instant fixedInstant, ZoneId zone)
    This method returns a clock that always returns the same time.
  • abstract ZoneId getZone()
    Gets the time-zone being used to create dates and times.
  • int hashCode()
    A hash code for this clock.
  • abstract Instant instant()
    Gets the current instant of the clock.
  • long millis()
    Gets the current millisecond instant of the clock.
  • static Clock offset(Clock baseClock, Duration offsetDuration)
    Obtains a clock based on the given clock with the duration added.
  • static Clock system(ZoneId zone)
    Returns a clock that returns the current instant using best available system clock in the specified zone.
  • static Clock systemDefaultZone()
    Returns a clock that returns the current instant using the best available system clock, converting to date and time using the default time-zone.
  • static Clock systemUTC()
    Returns a clock that returns the current instant using the best available system clock, converting to date and time using the UTC time-zone.
  • static Clock tick(Clock baseClock, Duration tickDuration)
    Returns a clock that returns instants from the specified clock truncated to the nearest occurrence of the specified duration.
  • static Clock tickMinutes(ZoneId zone)
    Obtains a clock that returns the current instant ticking in whole minutes using best available system clock.
  • static Clock tickSeconds(ZoneId zone)
    Returns a clock that returns the current instant ticking in whole seconds using best available system clock.
  • abstract Clock withZone(ZoneId zone)
    Returns a copy of this clock with a different time-zone.
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Java Lang Tutorial

In Java Lang Tutorial you will learn handy features of classes from java.lang package!

Java Lang Classes

Reflection

Java Lang Exceptions

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Java Util Map merge(key, value, BiFunction)

java.util.Map.merge(key, value, BiFunction)

The method Map.merge(key, value, BiFunction) associates given value with the given key or calculates the new value from the old value and the given one using provided remapping function.

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Java Util Map getOrDefault

java.util.Map.getOrDefault(key, defaultValue)

The method Map.getOrDefault(key, defaultValue) returns mapped value for the given key or defaultValue if there is no such mapping.

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Java Util Map forEach(BiConsumer)

java.util.Map.forEach(BiConsumer)

The method Map.forEach(BiConsumer) performs the given action for each entry of the map until all are processed or exception is thrown.

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Java Util Map computeIfAbsent(key,Function)

java.util.Map.computeIfAbsent(key, Function)

The method Map.computeIfAbsent(key, Function) computes the new value and associates it with the key if there is no mapping for the given key or the mapping is null. Returns the new value associated with the key.

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